Strange tranny problem?

I went to South Carolina a couple of weekends ago and my truck (98 Chevy Silverado Z-71 147K 5.7L) seems to shift out of OD at various times and then after awhile go back into OD (the RPMS would indicate this as such also) I had the tranny rebuilt 90K ago...Any ideas???

TIA

Steve

When has it shifted out of OD? Goin up hills, passing, ?
if you haven't changed the tranny fluid, you should do that. If it's not because of a load on the engine, it could be a sensor that is making the computer "think" that you've got your foot into it.

Is the tranny shifting out of overdrive (700 to 1000 rpm change) or is the torque conveter clutch unlocking (300 rpm change)

It usually does this on a straight and flat road, the RPMS will jump from 2000 to 2200 (at 70 MPH) and flushed the tranny 8500 miles ago...

sounds like your torque converter is locking and unlocking. Have the TCC solenoid checked.

Where would the TCC be located at?

Front of the tranny.

I have a 98 K1500 that is doing the exact same thing(has 217,000 miles on it).Is it shifting backwards like?If I step on the gas the RPM's go down and if I am at coasting speed the rpms will jump up all of a sudden.I have a code that reads P1810( TFP Valve position switch circuit)The TFP is trans fluid pressure.Also a P0756(shift solenoid B off

does the engine rev up like in neutral and then slow down and u hear a clunk or feel something catch and it goes after that, kinda like a clutch would do, cause that indicates a bad tranny my friends taurus did that and so did my lebaron i had before i got my truck. he had to get a 1600 dollar tranny rebuild and so did i. however my ex-gf's car was having some shuddering problems like that and it turns out a mouse bit thru the wire harnesses that help the tranny determine what gear to be in and that was all it needed. does anyone here think it is worth it to go buy a lockup torque converter for my 3 speed turbo 400? i always liked the feel of a direct connection and the better mileage too...

Is the TCC under the transmission pan?

Quote from 2000CAYukon:

You have to remove the pan to replace the TCC solenoid. Here is a picture of one http://www.4l60-e.com/#Performance%20Parts Look for part "#60" to see the picture.