My 88 245 automatic was running sluggish. Turned out the pre-fuel pump in the tank was bad. Had a reputable indy shop replace it since they diagnosed it and I didn't own the bung-nut tool.

It's been about 2 months and 1000 miles since the repair. Now it runs sluggish again, particularly under load like going up a hill. Starts right up. Gas tank is almost full. Main fuel filter was changed 5 months 󞪀 miles] ago. Idles smoothly. Shifts smoothly. Goes 70mph on flat road without difficulty.

Question: If the main fuel pump was "weak" [if there is such a thing] or inoperable, would the car even start? The shop wanted to replace both pumps because they say the main usually fails soon after the pre-pump. Before I take it back to the shop how can I check the pre-pump to see if it has failed again? Does the pre-pump have a relay? Other suggestions for places to check?
I can change the main pump myself but don't want to unless it is malfunctioning.

I guess what I am asking for is some trouble-shooting strategy.

[Plugs, wires, rotor, cap, air filter, fuel filter, flame trap were all serviced/replaced during the June tuneup 2k miles ago.]