Strange shift problems 1996 Z71 5.7

I hope someone can shed some light on my problem. I have a 1996 Silverado Z71 4X4 with 126k miles. I go out my driveway and to work the same way every morning. At one and one half miles from my house I get a check engine light and then my truck starts shifting strange with a very hard shift to second gear and the remaining shifts are fairly stiff. If I cut it off and then restart the problem shift quits but the check engine light stays on and then eventually with a little driving goes off as well. Also, at times the engine revs between second and third as if it can't tell when to shift. This has been happening since the weather got cool in the mornings. I have had this problem before and took it to a mechanic who replaced the throtle position sensor which cured the problem for a couple of months. I have had the same sensor replaced twice at 110.oo a pop. When I called him this time he said that it may be the main computer and I should take it to the Chev. store. I know I am looking at big bucks if I do that. I also get a high idle when this happens. I have changed the air filter and otherwise the truck runs great. Anyone got any suggestions. Thanks Wteachy

have you updated the computer with that wire from the dealer? its like 25 bucks

Could you elaborate on the wire. What is its function, what do I ask for? Is it something I can do myself. Thanks

You may have a problem with the valve body which is common on the 4L60E trans that is in your truck. The bore for the TCC plunger gets worn and the plunger hangs up cusing the torque converter to not lock up. When this happens the computer senses slippage and will up the pressure in the trans to compensate and this is what causes the hard shift. It usually sets a trouble code P1870 and turns the SES light on, But I have seen a couple act up and not turn the light on right away. I believe there was a recall fr some sort of ground wire for the trans and that is what the other poster is refering to. My vote still goes for a sticking TCC plunger. Most shops charge $250.00 - $400.00 to fix it.

id say go for the wire first its only 26 bucks, any dealer will install it for no cost....ill get the part number....the wire btw grounds out the transmisson.....

If your trans is shifting hard, you probably have a DTC code set on your vehicle. Have it scanned to see what the problem is. If it only occurs after driving at highway speeds for a few minites, I would bet on an 1870 code (component slippage). If so, find a shop that will either replace the valve body, re bore the valve body or block the valve in that cause the problem. Very common..
Tim
Trans tech 25 years..

I had the same prob. with my 97 Sierra w/ same trans. After I would
go past about 40mph it would slam into 2nd gear REAL hard and
shift erratic after that. Also, wouldn't go back into overdrive. I could
turn the truck off for just a second and restart and prob. gone.
After alot of research, it seems the guys here have it right about
the valve body guide wear. I also had an engine code P1870. It seems
most folks end up paying for a rebuild when sometimes just a bore kit is
needed. It was too late for the truck I had just bought and it needed
a rebuild and TC. The dealer paid for it. Good Luck!