400 rpm to high?

since monday morning the jeep has been running at about 2600 rpm at 65 mph in which before it ran at about 2250 at 65. i have no check engine lights on and all my connectors are plugged in. the fluid level is fine and not discolored. i run a large external coller so heat should not be a issue. the torque convertor is about a year old and the tranny is from a 98 with only 50000 miles on it. the only thing i have done to the jeep lately is swap a motor from a 96 about three weeks ago but it ran fine untill yesterday. any ideas would be appreciated. also if i let up on the throttle i can get the rpm to go down but the jeep gradually slows down.

Sounds like the convertor is not locking up.Check to see if it has thrown a code.Or a fuse is blown.
Mine will do the same thing if I flip the switch on the 1-2 shift kit(first gear lock-out).
Wayne

fuses were all fine and no codes but 12 and 55. you think the convertor might be on its way out. it was a rebuild from worldwide and i do have a spare from a 96 2wd aw4.

anyone else have any ideas

He didn't say the converter is on the way out. He said it isn't locking up. I agree that's the problem. Your mission (if you choose to accept it) is to find out why not.

Torque converter lockup on the AW4 is controlled electonically. Could be a fuse, could be a problem with the TCU, could be a problem with a solenoid. You might start by figuring out the wiring diagram for your year and adding a manual toggle switch to force the solenoid to operate. I know a person with an '89 who drove his for several years not realizing the TC wasn't locking up. Once he realized it, he couldn't find out why not so he added a toggle switch. He doesn't use the lockup around town, only hits it on the highway.

You can use it as a diagnostic tool, as well as a temporary correction while fixing the real problem. Just be sure to tirn off the switch when approaching a stop light.

well im glad today is my day off. if all else fails i have a extra switch on my acc block so i will wire it to the tcu tc lockup wire.
thnx guys

in the process of troubleshotting i found nothing wrong with any sensors. all three solenoids work and have the same resistance. next i want to eliminate the tcu i have a spare from a 96 is it interchangeable with my 91? i know the 96 does not have the power/comfort switch but is that the only difference?

i know someone out there knows if the 91 and 96 trans control units are interchangeable.

Does it happen when still cold or only after it warms up. My rig does that when the tranny starts to run to hot ands the clutches slip, kills my gas mileage. Install the biggest trans cooler you can find especially if you have 33" or larger tires.

already have a large b&m cooler. and i answered my own question earlier in that a 96 tcu will work no problem in my 91 i just drove 20 miles on it no problem except that it still runs to high rpm. i also wired a switch to solenoid three to supply constant voltage and it had no effect whatsoever. anyone think the solenoid might be going out.

is there a certian resistance or a way to test the speedo sensor to tell if it is going bad. i do notice my mph gauge twitch every once in a while but otherwise it works fine.