Once't upon a time I bought a new Mustang, 88 GT.

Ran great until I got a load of dirty gas.

The symptoms were similar to your pal's car except my probs would come in on level ground.
(Not many hills in Central California's San Joaquin Valley.)

The problem was the fuel filter was clogged.

After a few changeouts at about the 5000-10,000 mile mark (recommended is 30,000) the problem went away.

Try swapping the filter on the frame.