Check to make sure you have no vacuum leaks. u can use a cheap can of carburator cleaner and spray around the vacuum lines of the truck, if your truck starts idling up and changing, you have a leak then just replace the line. Older GM vehicles rely on Vacuum advances for the transmission and will not shift properly nor downshift if there is a leak. a lot of vehicles rely on vacuum to support many functions, mainly driveability as well as smooth running. there should be a vacuum line that runs near the rear of the transmission. also might want to check transmission fluid for the no power, cause even though you may have power in 1st and 2nd, 3rd gear is your main drive gear unless you have a 700R4 with automatic overdrive and it could be suffering from not enough fluid getting to the bands from the pump. also one more thing, check the downshift linkage cable the runs from the carburator to the transmission, make sure it is working, sometimes you can have a broken cable in the line and not even know it. hope this helps
SOURCE: Hesitation shifting between 3rd and 4th gears
yes i have heard of this and my friend is on the second transmission in his 2006 2500HD.the first time there was internal issues and the second time they ended up changing out the whole tranny.
SOURCE: 1998 jimmy 4wd wont shift
Fault in the gear box . This can be due to failure of the linkages, the shifters , the counter wheels or gears.
A fault in the gear box can be speculative and so unless the gear box is opened this cannot be confirmed.
You will need to decide if the job can be done with the tools and facility you have within your limits.
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Hi Bruce Ellsworth, I want to help you with your problem, but I need more information from you. Can you please add details in the comment box? Th350c transmission or th700r4 (4l60e)
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