We have a 1986 F150 XLT with a 351M. No 4WD, no computers. It shifts into low gears and reverse but not higher gears. We changed the fluid and found a small white plastic mushroom shaped plunger thing with an O ring in the pan. We can't figure out what is wrong and if we need to just get it rebuilt or replaced. Any advise?

 

The mushroom thing is just a filler pipe plug used from the factory, don't worry about it. Check the grommets on the TV cable. I bet you have a bad one.
Alan

 

Check the vacuum modulator line at both ends. It may have come off. If the hose is soft and mushy, the modulator is probably trash. Check the kickdown linkage also.

SL

 

Is the kickdown/tv cable working properly?