Luxury sport shifting problem

[lakewood213]

im brand new to this site, and have issues with my monte that maybe someone can help with. thanks in advance for taking time to reply with any helpful knowledge.
I have an 87 LS 4.3 with overdrive (not sure what number the trans is). after driving the car for about 20 minutes the trans downshifts rough, then when accelerating, the trans starts to take longer when upshifting through the gears but shifts too early, meaning it will go into overdrive at like 40 mph.
any additional info I may have left out, let me know, thanks

 

[tetomas]

First thing to check is the throttle valve(TV) cable. It hooks on the side of the carb or throttle body, and goes down to the trans. With the engine turned off, push the release on the TV cable end at the carb, then push the inner liner all the way toward the firewall. Now push the throttle wide open, the cable will self adjust with a click. Also would not hurt to do a fluid and filter change.

 

[jlcustomz]

May want to give a can of Lucas trans fix a try. It won't overhaul a completely shot transmission, but the cleaners in it may clean up some sticking parts & give an old trans a little more life before a rebuild.

 

[lakewood213]

much appreciated on the feedback. I now have a starting point. the car is a low mileage car, so I am hoping those low miles weren't hard enough driven to ruin the transmission. I will update as I go through your recommendations. thanks

 

[lakewood213]