Well not to easy to diagnose "occasional skip".
There are only 2 reason but several possible causes.
Fuel or spark are the reasons
For fuel:
Perhaps fuel pump is losing power momentarily, could be fuel pump relay, but that would seem odd to occur only under load in a specific RPM range.
TPS, throttle position sensor, this is a simple variable resistor like a light dimmer or volume control, and it is a mechanical device so can get "dead spots".
It could have a dead spot that you would only notice at a certain RPM range and only under load since you wouldn't feel it otherwise.
Best way to test TPS is with a volt meter and sewing pin(needle)
It will have 3 wires
Top wire will have 5volts when key is on
Center wire tells computer the position of throttle.
You want to test top wire first, use battery or engine metal as ground
Use pin to pierce wire to test "+" voltage, do the same for center wire.
So you test it with wires still connected to TPS and key on/engine off
Center wire should have .69-.99 volts when throttle is closed, under 1 volt.
As you slowly open the throttle manually the voltage will increase, look for jumping or dropping of voltage as you open throttle, replace TPS if you see that.
At wide open throttle voltage should be 4.5 or higher.
If voltage changes rapidly(jumps or drops) computer thinks you let your foot of the gas or pressed to the floor, either will cause stumbling, since throttle plate has not actually changed position.
Clean MAF(mass air flow) sensor and check its connector, RPMs have a specific air flow for engine size, i.e. a 3 liter engine will pull in a certain amount of air at a certain RPM, if MAF sensor was not reading air flow correctly at certain levels then engine could stumble, again you wouldn't feel this unless under load.
Spark is harder since computer controls it all after 1994, no separate modules, just coil and spark plugs.
There are 3 separate coils in the coil pack, one could fail and cause the stumbling, but would be harder to be RPM range specific.
But it could happen, a weaker spark has a harder time igniting a Richer mix, and when accelerating the mix gets richer, so could cause stumbling until mix leaned out a bit.
Video here on testing coil packs:
www.youtube.com/watch?v=c1zhgsnyZWw
Problem with testing coils is that a bad one will test bad, but a good test doesn't mean "good", lol, because of the low OHMs even a little heat can cause problems if a coil is starting to fail, so worth testing but doesn't mean 100% good