Question for the troubleshooting experts:

My 1988 wagon(5 speed manual) has developed a hesitation when I'm accelerating, particularly in first and second gear. I've come to the conclusion that it's cutting out and not just a misfire. The car has over 425k miles on it. I've owned it for almost five years, so I don't know the previous history of what's been done to it.

It runs good when the engine is cold. After about 10-15 minutes of driving, it cuts out bad when I accelerate from a stop under moderate to heavy throttle. once up to speed it runs ok(but it seems a little weaker on power than when it's cold.

I did clean the throttle body about a month ago, as well as a tune up(plugs,cap, rotor). I did replace both fuel pumps a couple years ago, along with the strainer/filter. I checked both pump a couple weeks ago and again replaced the screen on the pre pump and the fuel filter(both pumps checked ok).

Any help is appreciated.