I drove home a 175,000 mile ’05 F150 4.6L that I bought last month at an auction and a 40 minute highway ride ended up a 2 hour trip on city streets. It’s got no reverse but I’d be happy if that was all that was wrong with it. It won’t stay in gear above 30 mph unless you are accelerating. If you accelerate to say 50 mph and back off the gas, the next time you step on the gas the engine just revs like its in neutral. If you want to accelerate, you have to coast down below 30 mph at which point the transmission will engage and you can get back up to speed and do this all over again. It says TRANS FAULT in the display and the O/D light is flashing. Any ideas?

 

You need to go get the codes read. The inexpensive scanners that the parts stores use for their free service are not capable of reading the trans codes, you will need to go to a dealer, trans shop, or a well-equipped garage.