Transmission won't lockup

[Marlin]

I've noticed in the past two days that my transmission won't lockup above 50. It will lock up for a mile or so but then the revs jump to about 3k and stay there. Changed the fluid and the symptom persists. Currently resetting the truck via battery disconection.
other than this my transmission works perfectly. Please help.

Thanks

THere are also shift solenoids. That is what my tranny started doing, started with slipping out of 4th, then it wouldn's shift into 4th, then it continued on into 3rd, and at that point it was time to do a swap. I hope yours is just the shift solenoids...good luck.

[creeg]

This sounds similar to a problem I have been having, which seems to have gone away as of late: I had an issue where I would be driving on a flat surface, and then back off the gas and coast. If I happened to hit the gas again at about 24 mph, the engine would rev and not engage, almost like it was in neutral. I would have to let the car coast a bit and drop down a couple mph before it would engage again.

Is this possibly a solenoid?

Thanks