Hello, and welcome to JA!! very possible both are related, I am going to post two possiblities of what might be going on here. this is some info from GM
Code P0872 or P1711 setting soon after a transmission repair. Generally, the vehicle did not exhibit the code prior to the transmission repair.
Investigation into DTC P1711/P0872 has shown that in most cases trucks that set this code have had a cracked transmission adapter housing. Bulletin 03-07-30-031 contains details on the adapter housing repair. Cracks in the adapter housing can allow dirt and sand to enter the transmission resulting in stuck shift valves in the valve body. To reduce the possibility of setting a DTC P1711/P0872 when repairing a cracked adapter housing, the following five steps should taken:
By reducing the amount of dirt and sand inside the transmission, the chances of setting this DTC will be greatly reduced. The following checks help in determining the if shift valve "E" is stuck in the bore or shift valve "C" has a oversize bore or if the condition is related to the wiring.
Cycle the ignition key to the run position with the engine off, the TFP (Transmission Fluid Pressure) switches "C" "D" and "E" should all read OFF on the Tech II scan tool. Upon starting the engine the TFP switches "C" "D" and "E"should change from OFF to ON The above 2 steps indicate that the TFP switch, wiring and TCM are functioning properly Once the transmission reaches a Steady State first (1st) gear the TFP switches should read"C" OFF "D" ON "E" OFF, if "E" does NOT change to OFF once the transmission has reached a steady state first (1st) gear the "E" shift valve may be stuck in the bore or the "C" shift valve is loose in the bore causing a bleed action to the "E" valve. This will force the "E" valve into the ON position once this occurs DTC P1711 or P0872 will set after 2 seconds. The valve body assembly should be checked for a stuck valve and rear cover should be replaced (if cracked) as required for this condition. The valve body should be torqued to 100 inch pounds. Over torquing the Transmission Fluid Pressure Switch (TFP) may result in shorting out the TFP and setting DTC P1711 or P0872.
If the "E" switch changes to OFF, the condition may be intermittent and the DTC flow chart should be followed to see if another condition can be found for the DTC P1711 or P0872.
#02-07-30-011C: Slow or No Engagement of Automatic Transmission, No Start, Blank PRNDL Display, Flashing PRNDL, DTC P0708, P0872, P0847, P0875, P1711, P1713 or U1000 Set (Diagnose Condition, Repair) - (Jun 21, 2004)
Some customers may comment on one or more of the following conditions.
Moisture contamination within the Park Neutral Position (PNP) Switch may cause this condition. This is sometimes referred to as the Neutral Start Back-up (NSBU) Switch. On a left turn, water spray from the left front tire is directed directly at this switch. Proper installation of the "Front Shield" and "Rear Shield" are essential for proper repairs.
This bulletin ONLY applies to vehicles equipped with a two connector PNP switch as shown above.
A complete and through diagnosis must be performed by a qualified electrical technician to determine the cause and avoid needless replacement of good components.
Important: The Transmission Control Module (TCM) and or the Pressure Switch Manifold (PSM) should NOT be replaced unless properly diagnosed. They are probably not the cause of the concern. It is often assumed the module is the cause of the concern when, in fact, it is another component or the wiring between the components that causes the concern.
Important: Remember, everything starts with a properly operating Neutral Start Back Up (NSBU) switch. The NSBU switch has been incorporated into what is now called the Park Neutral Position (PNP) switch. If the PNP switch does not provide the proper voltage signal to the module indicating the transmission is in either Park or Neutral, the module will not allow the starter operation. After the engine is started, and the shift lever is moved to either Reverse or one of the drive positions, the range selected portion of the PNP switch portion provides a voltage input to the module as to what range the driver has manually selected for transmission operation. The module then controls pressures, shift points and other transmission functions based on the voltage input received from the range portion of the PNP switch.
The technician may find one or more of the following conditions. The list of these conditions does not imply any type of frequency or order. They are random events and may occur in any order.
A blank PRNDL display may indicate a condition with the PNP switch and/or one or more of the four signal circuits from the PNP to the TCM.
Or, a blank PRNDL display may also occur if an out of line condition exists with the Serial Data Circuit (CKT 2470, yellow wire) from the TCM to Splice Pack 205.
If the Gear Selected display does not match the shifter position in the vehicle, diagnose using one of the following methods.
The PNP switch, as referenced in SI, is known as the NSBU switch in the Parts information. It is now serviced with a Park Neutral Position Switch Kit, P/N 29540479.
A flashing PRNDL display may be the result of incorrect sensor inputs or transmission abuse protection modes being received by the TCM. The following are some of these conditions:
Transmission abuse protection modes are encountered when a customer performs one of the following types of maneuvers:
When the TCM encounters any one of the above conditions, the TCM will flash the PRNDL and default the transmission to Neutral. A flashing PRNDL indicates something is/was incorrect. The transmission may need the attention of a qualified service technician.
Important: If the old PNP switch will not slide from the selector shaft without the effort, the selector shaft may need to be filed to remove flaring on the end of the selector shaft. This is important, installing the new switch onto a selector shaft that has damage will cause damage to the new PNP switch.
Important: If the new PNP switch will not slide onto the selector shaft easily, the selector shaft may need to be filed to remove flaring on the end of the selector shaft. This is important, installing the new switch onto a selector shaft that has damage will cause damage to the new PNP switch.
Tighten Tighten the bolts to 27 N·m (20 lb ft).
Important: Installation of the front shield and rear shields are important. Without proper installation of the shield, a return repair is probable. Follow all directions as listed on the installation instructions sheet included in the Switch kit, P/N 29540479.
Tighten. Tighten the nut to 24 N·m (18 lb ft).
Switch kit, Park Neutral Position