I have a 2008 F150. Lots of history on the transmission. Been "rebuilt" several times by a somewhat questionable shop with lots of overheating problems. It wound up being the in-line thermostat which I completely removed and bypassed. That was all done about 2-3 years ago and it has been running fine since then. Recently, it started slipping out of first gear. At first it only happened once it was warmed up, but now it does it when cold as well.

When I shift into drive, it will slip out of gear. If I give it a little gas, maybe 100-200 rpms over idle, it will pop back into gear pretty hard. If I shift into first, it will go into gear normally. It does this if I shift from park or reverse, into drive.

If I shift into first, it will not slip at all. I can also shift from first into drive after going about 15-20 feet and it will drive normally, never slipping out of gear unless I put it in reverse or park.

Other than this, it drives normally. The fluid look and smells normal and is full. It is not overheating at all according to my scanner. I called a couple transmission shops and they just want to rebuild it again for $1500-$2000. I have also thought about just swapping it with another used one, but that seems to be asking for more problems. Any ideas.