Try and free rev that engine to redline.  If the engine goes to redline easily, then I would guess the fuel pressure would be ok.  If not, then another indication the fuel pump starting to go bad.  But without an actual fuel pressure gauge, it would be sort of difficult to weed it out or not.  Also, if you could pull the vacuum line on the fuel pressure regulator and listen to the engine idle go up a bit and see it also on the tach.  With a fuel pressure gauge it should jump up roughly 10 psi.

As far as the clutch goes, it could be a problem especially if the clutch is slipping.  That would cause the similar feeling to no power.

If you know the clutch is slipping, take care of that and see if it helps.

It might only need adjustment.  If it's worn or damaged, then of course replace it.

The clutch slipping can cause damage to the transmission by requiring you to shift when the engine RPMs and gear box are not in sync as intended.  It can also cause extra strain on the engine from running the RPMs up to compensate.

Let's say you should be shifting to 2nd at 15 mph.  If you can't get the speed up to 15 without revving to extra RPMs,  the transmission and engine are not in sync.  It may actually feel like you are down shifting, because the transmission will become a drag on the engine.  Basically the engine is running faster than it should be for the gear you're in.

Just a thought!   

IIRC, that year make and model, it has a hydraulic clutch master cylinder and a non-adjustable/self adjusting internal hydraulic slave cylinder.

Another thing that would give the same symptoms as lack of power would be, the brakes are dragging.  Can you roll the vehicle easily with the transmission in neutral after a long drive?  The reason I ask is, when the vehicle is driven the brakes(rotors and drums) heat up and they expand a bit, creating a tighter tolerance to the brake pads and shoes.  Any burnt brakes odor after a long drive?  If one can't push the vehicle after a long drive while vehicle is in neutral, jack up each corner and spin the tire.  If one of the fronts are locked up it could be either a hose or frozen caliper.  If one of the back is frozen, either severe rust/sand/dirt build up in drum or a frozen wheel cylinder.

finally figured it out and got the truck fixed and running great.
it needed a new tune up
changed coil pack.
one injector was bad. -hesitate off the line problem
changed thermostat
changed fuel filter
a shop tested and back pressure was extremely high
cat converter was plugged, rattling, screens were broken inside.
changed the whole exhaust system.
truck is running great now.
still gotta do clutch at some point soon.