Keeping the fuel tank at least half-full could improve things. I say this because the symptom could be caused by a bad in-tank fuel pump, or by bad hoses or wiring to it. Also because I know some youngsters who like to drive around with a near-empty tank, and think nothing of it.

There are two pumps, one inside the tank and one outside. The in-tank pump merely supplies fuel to the second (main) pump. When the tank is low, the in-tank pump does the work of pulling the fuel out of the bottom and keeping the main pump supplied. When the tank is more full, the main pump is usually able to suck what it needs from the tank without assist. Hill climbing and a heavy foot on the pedal require more fuel per second. If the in-tank pump isn't working, he'll feel the problem then.
--
Sven: '89 245, IPD sways, electric rad. fan conversion, 28+ mpg - auto tranny. 850 mi/week commute. '89 245 #2 (wifemobile). '90 244 (spare, runs).