TJ "conks" out at 75 mph

[AJeep99]

A few weeks ago, my 2000 Wrangler Sahara (50k miles, 4.0L, auto tranny) started holding second gear longer than usual before banging it into 3rd. I noticed this would happen under hard acceleration.
My real concern began when I was heading home from work one day and I was on the highway holding 75 mph constant for about 10 miles when all of a sudden the cruise control kicked off and my Jeep started coasting. I put my foot back on the gas and even pumped it but I could not get any throttle response (even though the engine was still running, the RPMs would not even jump) until I amost came to a complete stop. While coasting at about 20 mph, the vehicle was able to respond to my foot pressing on the accelerator.
I brought my Jeep in to the dealership and they test drove it and could not find any problem with either transmission or throttle. Keep in mind you can only tell the transmission has a problem under hard acceleration, under normal driving, no problems seem to arrive. Anyways they didn't find a problem so I had my transmission fluid flushed b/c it was close to its scheduled change.
Last week, my Jeep experienced the same problem on the highway, it cut out after doing 75 mph for a about 8-10 miles of constant driving, this time I did not have the cruise control on and the Jeep did not kick back into gear until I decelerated to about 20-30 mph. I don't want to mislead you guys into thinking that at 75 the vehicle stops, I took it up to 85 the same day it cut out on me, it just appears that when holding a high speed for a long time, it just cuts out.
This problem is a major concern b/c I can imagine it being a problem with a bad sensor or relay in the computer only I have no clue where to start and the Jeep dealership thinks I'm imagining things or something. I was wondering if abybody could provide some insight or have a similar problem that was resolved.

Thanks

[fredjacksonsan]

Smartass answer? do 74

Seriously though, it does sound like a sensor is having trouble after a long highway run. I'd take a look at the camshaft position sensor, the crankshaft position sensor, and the throttle position sensor.

Also, have your dealer put it up on a rack with you there, and run it at 75 mph until the problem appears. They should be able to have it hooked up to diagnostics when it happens.