1991 4 cyl overheating

Hey all,
A friend has a 1991 pickup 4wd w/a 4 cyl. 140,000 miles It has been
overheating constantly recently. He has replaced the theromstat, and
many waterpumps( after he bought and tried a rebuilt, he bought a new
generic, then a new Toyota w.p.) to no avail. The radiator has been
rodded for clear passages.
He can drive it easily around,w/o incident. Unfortunately, the road to
his home is uphill about 1.5 miles, by the time he geta back home the
truck is spewing it's guts. I thought there might be a head gasket
problem.

Is there anyone else that has this problem??? could there be an inherent
design problem??

Any comments or thoughts would be appreciated

Thanx in advance