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Gary
Gary, ASE Certified Technician
Category: GMC
Satisfied Customers: 15728
Experience:  GCM master tech over 25 years
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Got a 2000 GMC Jimmy, 2wd. When I first drive it in town and

Customer Question

Got a 2000 GMC Jimmy, 2wd. When I first drive it in town and highway, shifts fine for about 15-20 minutes. I am guessing time for it to warm up. On the highway, it will downshift in third I believe after running about 60 mph for a few minutes, and will not shift any higher. I believe its 1-2-3-o/d. In town, can drive for about 15 minutes before in goes back to second gear and will stay in second even when I come to a stop and start back up. I can put it in 1st gear, but anything else stays in 2nd gear. If the truck sits for a 1-2 hours or so, it will start to shift fine again. No transmission related codes for check engine light.
Submitted: 9 months ago.
Category: GMC
Expert:  Gary replied 9 months ago.

how long since the fluid was flushed ?

has anything been done yet to correct this problem ?

did this problem start out of the blue one day ?

no codes at all ?

Customer: replied 9 months ago.
I got the codes read. Only a misfire code came up for one of my cylinders. that has been corrected, still have the same issue. fluids have been flushed 2 weeks ago. started a couple weeks ago.
Expert:  Gary replied 9 months ago.

did the transmission flush help at all ?

was the pan pulled yet ?

Customer: replied 9 months ago.
did not help. Pan was pulled, filter changed, I was recommend to take those steps first. still having same issue, no difference.
Expert:  Gary replied 9 months ago.

any access to a scan tool to view live computer and transmission data ?

with NO codes the odds of the transmission loosing its power for the solenoids is very slim

are you sure its 4th gear or is it overdrive or lock up that goes out first ?

Customer: replied 9 months ago.
no access to scan tool. My gears go as this. P-R-N-D-3-2-1. In "D" is when this issue occurs. I can put it in "1". Once the issue starts though, putting it in 2-3-D don't change the gears, feels like it stays in 2nd. and can only change it to "1". and R , N, and P of course.
Customer: replied 9 months ago.
I don't understand fully how solenoids work, but I was thinking if they worked fine at the beginning, what would cause them to fail after 15-20 minutes of driving. And this replicate each time I drive same exact situation without change, every time.
Expert:  Gary replied 9 months ago.

if we had a wiring issue or even a solenoid issue it would set codes

with no related codes the computer is shifting it and has the correct resistance and feed back from the transmission as it would trigger codes

this issue is going to be more so a problem internally with a forward srag one way clutch which will cause this type of issue and they love to act up when warm and be fine cold

the best action with no codes and a good flush done and the pan removed and checked for debris would be to drive it with a scan tool and shift the transmission with the scan tool if the scan tool says its in the gear but the transmission physically is not then that is more than likely our issue

if you have any questions please ask as i do not get credit for my work until you rate us here at justanswer

Customer: replied 9 months ago.
Could anything related to speed sensor, TPS or vacuums cause this problem? asking because after reading a lot of forums, was leaning towards one of these, but wasn't sure.
Expert:  Gary replied 9 months ago.

usually those would set a code

if the speedometer works fine and with a scan tool the TPS shows a full smooth range from idle to wide open throttle its not likely those are not the issue

Customer: replied 9 months ago.
I also saw something about the transmission fluid pressure switch also, would that cause something like this?
Expert:  Gary replied 9 months ago.

not usually that would set a code or cause the transmission to slip