2.8 won't cruise...

My 86 XJ has a 2.8 V6. So far it's been great; reliable, economical (25 mpg) BUT...

Last time I took it on the highway it started to hesitate and cut out once I would hit 60. Didn't matter if it was in 4th or 5th. Lots of hesitating. If I dropped speed things would smooth out.

Fuel pump? lousy carb? I checked the fuel filter on the Varajet, looked as good as it did when I last changed it.

Please help, I'm ready for a color change...from grey to fire!

Sounds like a fuel pressure or volume issue.

I'm guessing the reason you only see the problem in 4th and 5th is because in the lower gears, you accelerate through and let off before the carb bowl empties out, and when you let off, it has time to refill. Try taking it out on a straight stretch of road(not freeway) and see if it will do the same thing if you hold it in 3rd at the same (cruise) engine RPM for a minute or two.(bet it does)

Cold be the fuel filter(You said it looked good, so assuming it is,...)
Pump could be going south. Unless you have a pressure test gauge, it's hard to tell. You can try disconnecting the fuel line at the carb and putting it in a container, then crank the engine with the ignition disabled to check the volume output of the pump.(dangerous, be careful doing this) The Chiltons manual for the Cherokee has a pretty good description of the procedure.
There's also a debris screen in the fuel tank on the end of the pickup that could be clogged.

I'd say replace the filter anyway, then test the pump if the problem doesn't go away.