1997 Olds88 3800 w/ 4T60E trans ~100,410 mi
I've been chasing a P1071 problem for a couple years w/o much success; changed darn near every engine component. Last year I noticed that the motor oil was 1' higher on the stick than full so I checked trans fluid and it was 3 1/2 qts low. No one would take me seriously. Eventually I had the trans rebuilt with all updates at 100,210mi and it worked great for the couple weeks we drove it but p1071 persisted so I parked it for a a few months; I ran it for 1/2 hour twice in Neutral while parked.
Today took it out and trans was slipping cold but got better with heat. I checked and the motor oil is above full again and the trans fluid (warm) is below the low hole on the stick- milage= 100,440. I'm not imagining this! I can't see how t fluid could get to motor via seal problem especially since trans is fresh so I'm thinking that somehow there is a vacuum line sucking it into the motor. Does anyone have any idea as to where this could be happening? I can't help but think it might also have something to do with the P1071 & idle miss as well.

I meant that the fluid initially was 1" above full--not 1 foot.

Welcome to the forums.
As temperatures rise from driving, the trans fluid will also rise, keep an eye on it.
Under filled state is not the best scenero. I like to see the trans fluid on my Buick slightly above the dot when hot.
Have you replaced the upper & lower intake manifold gaskets?
One of our Gearhead members may have a better idea what is going on, I did find this thread about the P0171 code.
https://www.gmforum.com/oldsmobile-1...1-code-302197/

Are we really talking about a P1071 or is it a P0171?

If it is a 4T60E and not a 4t65E, then it has a vacuum modulator. If the modulator is allowing transmission fluid through from the hydraulic side to the vacuum side, it will get burned by the engine as part of the combustion process . . . will reduce your transmission fluid level. Quick test: disconnect the vacuum line from the vacuum modulator. Does it have transmission fluid in it or is it dry?

Either way, if the rebuild is only 200 miles old, take it back to the rebuilder.

I don't see a way that transmission fluid would get added to the crankcase. I'm not saying that is isn't happening, just that there isn't a way that I know of for it to happen. On a car with an oil-to-water cooler, I could see where a Rube Goldberg sequence of events might make this possible by way of the cooling system, but then there'd be much worse problems. In any case, your car doesn't have an oil-to-water cooler unless an aftermarket unit has been added.

Thanks for the responses, Guys. The P0171 issue has been going on for nearly 3 years now and I've done both U&L manifolds as well as changing out nearly every component in the system-electrical and mech. Mapsx3 O2 sensors x3 coils; injectors; blah blah. I think it MIGHT still have the original TPS but not much else. I'm not imagining the fluid transfer. It happened twice prior to the rebuild and has again with only a couple hundred miles of driving BUT it was run for 30min or so twice while it was sidelined so that adds to my suspicion of it being a vacuum problem (which might be a factor to P0171 issue also.. I'm taking to trans shop as soon as I finish this post. I'm just hoping someone might be able to shed some additional light on this so please keep the thoughts coming. Thanks.

Let us know what the trans shop discovers.
A smoke machine is the best & quickest way to discover any potential vacuum leaks.

Found a compromised vacuum 'T' this AM--contribution unknown. No T fluid in vacuum lines from transmission. Fixing vac leak and xing my fingers.

Good news the T fitting was found.With any luck, hopefully you may be good to go.
Did the trans shop check & clear the code after the fitting was replaced?

That has a good chance of fixing the PO171.

Awaiting new part but temp sealed the 'T' and engine runs better. Waiting to see if the code self clears which should happen if the 'T' was contributing to code. Trans shop checked and felt the tranny fluid level was correct but had no explanation as to why oil was above full mark--neither do I.