Truck Repair: 1995 chevy silverado 4x4 sputtering and loss of power under load, throttle position sensor, chevy silverado

Question
This truck has over 166,000 miles. not sure waht has been done to it bought it 4 months ago from a dealership.

While towing a boat up a approx 3% grade the engine started to sputter and acted like it was not getting fuel at about 40mph and in 3rd gear. I took my foot out of it and slowd down to about 30 and as long as i didnt accelerate it was running fine then it got worse still going about 30 so slowed down to 20.. eventually the hill was over and the truck ran ok as long as i didnt try to accellerate hard. launched the boat no lack of power pulling it out of the water. started back up the grade and got so bad that i could not go above 10mph and in 1st gear..
luckily it made it home.. sputtering and popping whenever trying to accelerate, i just eased my foot out and the sputtering stoped.
Sorry for the long story but more info is better than none.

Question: Is this fuel, or spark related. Searches have led me to believ possible fuel pump, egr, filter? any suggestions?

Also please note that as long as the truck is not under load it runs fine. acceleratin is quick and responsive..

Answer
What I would do is connect a fuel pressure tester so I could see it while driving, and then go for a ride, prefferably with a load.
Find out what the pressure should be for your type of injection, and then watch. If the pump is working correctly, the pressure will stay the same.
If the pressure drops, and causes the sputter, then change the filter, and go again.

Other possible causes are the throttle position sensor, water in the gas, then electronics.
But check the fuel pressure first.

I have also had hose connections INSIDE the tank, that would allow the pressure to be too low. Would idle fine, but jump and buck under load. The hose had a split in it, so if you end up inside the tank, check that before buying a new pump.

Van