I have a 1998 F150 with auto lock 4x4 and a automatic transmission. The problem I am having is after setting for about a week I drove it and 1st to second shift normally but when the RMP's/MPH hits time ti shift to third I get RMP increase and no third. I have shifted it manually 1 then 2 and into drive same result RMP's increase just like it is in neutral.

Miles on trans is about 120K have been serviced about 10K ago with no poor color or smell. Mechanic said transmission and filter looked good no metal or junk in oil.

I drive down the road and it shifts from first into second then about 35-40 it hits what should be third but nothing free RPM's. I let it slow down to below 35-30 second kicks back in and away we go again until it's ready to shift into third.

I have been told possible speed sensor problem, possible other sensor problems looking for leads on where to look and what items to check. Just had Shop Mechanic drive it and he was baffled for everything looks good that he checked such as oil, and how it drove until it tries to shift into third. No over drive light flashing or anything and no engine codes showing at all everything clean in memory.

Thanks in advance!,
Keith

 

I think you need a rebuild. ):
I had the same thing happen to 3 of my 4R70 trannys.