Cars - 1997 Jeep Cherokee hesitates after warmed up......

I have a 1997 Jeep Cherokee (4.0L/6 cyl) that has a problem with a
hesitation on acceleration first thing when I drive it in the morning
and when the Jeep has been parked and then driven again within 1 - 4
hours of being parked. I've just replaced the spark plugs and the
problem is still there. I run ethanol blended fuel and have not had a
problem with fuel economy since I've owned it. Also, I've tried
running fuel injector cleaner several times to break up the deposites
(if there are any) and to no avail. Usually when I start the Jeep in
the morning it's fine - until I get about a half block away from the
house. It'll hesitate for a few seconds and if I pump the accelerator
a couple of times it will respond and then it may not happen at all -
straightens right out. When I park the Jeep in the lot at work and
then go back out to run an errand at lunch the same problem happens -
hesitates until I pump the accelerator a few times (and in some cases
I'll hear a backfire in the exaust at that point) then it straghtens
right out and will run fine the whole time. There are some instances
where the idle is rough and it may even stall - but that's not very
often. Usually if it stalls, the idle seems like it's set too low and
it'll die at a stop. I did a check on the plugs, too, and didn't see
any tell-tale signs of fouling - they looked worn, but not oily, wet or
carb'ed up. Also, I don't have any signs of antifreeze in the oil or
vice-versa - so this isn't some heat gasket leak either - at least it
doesn't show signs of that.

Any help with diagnosing this will be greatly appreciated. I love my
Jeep but I hate how it runs when it's been parked for awhile - - HELP!!