My 90 did that with timing out by 2 degrees!

Assuming it's not that I'd check the coolant temp sensor, fuel pressure, exhaust for leaks, O2, and MAP... this is a job for a multimeter!

I could help narrow it down:
Where in the RPMS does it cut out?
Does it stumble (shutter) or just bog?
What if you stomp it and grind down the peddle?
Are you kicking down?
Heating up?
Does being in OD make a difference?
Is it slow, bogging, stumbling... otherwise or only on hills?