Hello GM has a document on your issue for the code P0894 about the transmission slipping.The torque converter clutch enable solenoid has been found to be cracked down the side of it and has to be replaced along with the wire harness. I'll post the document below.
#06-07-30-007A: Malfunction Indicator Lamp (MIL) On, Diagnostic Trouble Code (DTC) P0894, Harsh 1-2 Shift with 4L60-E, 4L65-E, 4L70-E Auto Transmission (Test/Replace TCC Enable Solenoid/Harness, Auto Trans Wiring) - (Feb 20, 2007)
This bulletin is being revised to add part number for vehicles with Input Speed Sensor (ISS). Please discard Corporate Bulletin Number 06-07-30-007 (Section 07 -- Transmission/Transaxle
Some customers may comment on a harsh 1-2 shift with the MIL illuminated.
Diagnosis with a scan tool may reveal a DTC P0894.
This condition may be caused by a leaking TCC enable solenoid. The TCC enable solenoid is part of the automatic transmission wiring harness.
Follow the diagnosis and repair procedure below for a DTC P0894.
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Your truck uses a throttle actuator control which is incorporated into one and it eliminated a separate throttle position sensor. The P0894 is a specific code internally to the transmission.
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ok thanks so much sir... youve been a big help