transmission??

hi,
i am having trouble with my tranny slipping out of overdrive. i have a tech that says he thinks it might be the computer, but i don't want to fork out the money unless i am sure. I know there is nothing wrong with the transmission itself. its been inspected inside and out, and i fought that battle already for over a year. the problem is NOT getting worse, its just been doing the same thing for about two years now. When ever I am cruising along, no matter what speed i am going, as long as the car is in overdrive, occasionaly it will slip out and feel like it is in neutral.. to fix this, i can manully downshift to third, and then shift back up to Drive and it will be fine for a little while, until it does it again.. This is not a problem that is putting be on the side of the road, but it is very bothersome and irritating to have to deal with. Does anyone know what could be causing this? could it be bad wiring? could it be the computer? again, i know there is nothing physically wrong with the tranny... any ideas would be of great help... I have a 1998 LS1 z28 with 700R4 automatic tranny (4 spd + OD)
Thanks for any help...
Jeff

700R4??? I thought the 98 has a 460le or what ever they call them now adays

that was posted by my older brother if you were getting confused

How many miles are on the transmission?? If it is a 4l60e like it should be, I guess its possible that the comptuer could be messing up its shifting because its electronically controlled but Im not sure if just a computer problem could cause that.

140,000 miles total

and it is 4L60 (700R4)

The 4L60E in my '95 S-10 is doing that. It's the lock-up torque converter thats bad on mine... BTW....I also have a '78 1/2 ton chevy pickup and last sunday the nut that holds the shift linkage on the trans fell off. I stuck the linkage back on and figured I'd fix it when I got home and forgot about it. Don't ever forget! So...the next time it fell off I hit a bump racing a rice burner(old rust bucket pickup got a 383 stroker in her) and it shifted into reverse at 90+ MPH. That was interesting...blew the drivers side floor out, broke the trans off the motor and tore the cross member out and dropped the trans and driveshaft onto the interstate. I thought I hit a land mine....lol Truck has my spare trans in it and a new floor the next day....and they ask why I keep spare parts cars around.......lol

thats very interesting, but that sounds like something pretty harsh, the problem with mine is it is a very suttle, and you can't even really notice that it has slipped out of gear until you hit the gas and the engine rev's up. and also, this only happens in overdrive. one more thing, my throttle positioning sensors have (from time to time) thrown low voltage codes, could this have anything to do with it?

if you have a stock 98 than you have the 4L60E, just to clarify...

sounds like three possible problems,

first the most simple, your torque converter is going bad

second, your TPS is going bad.

third, there IS something wrong inside the tranny

you see, the torque converter lockup is controled by several sources of information, throttle position, vehicle speed, engine rpms, all that. so if one of those signals changes from the window the computer wants to see, then the converter unlocks, leading to a rise in engine rpms.

now if its completely going into neutral, not just a rise in rpms, as if the tranny is completey disconnected that means that the problem is inside the tranny. When it was inspected was it just a visual inspection, or were all parts tested for operation?

I think it is the TPS also. No, its will not go completely into neutral, just like you said, a rise in rpms, (seems like neutral, but still has a small (very small) amount of pull to it) it was visually inspected, and even though the my tech didn't think it needed it, he replaced all the springs in it, but said he REALLY REALLY doesn't believe that there is anything wrong with the tranny, and my tech works for a chevrolet dealership, so he is pretty good, but even this has him sorta stumped. He thinks its the computer, I think its TPS, but we both agree we don't think the tranny is bad. so whats the difference between the 4L60 and the 4L60e anyways?

Thanks,
Jeff