One very obscure possibility is to check your O2 sensor...

I had a 30 sec. stuttering problem after the car ran for 3-5 min.....

then it would act fine again ....

turns out my O2 sensor was physically broken off (half of it is probably still stuck in my exhaust somewhere!)

anyway... if I understand what happens the ECU tries to run off of the O2 sensor's input for awhile before it gives up and starts to ignore the failed sensor...

while it's reading the failed sensor's input it runs like crap.

others will have less obscure answers (check flame trap, AMM, etc.) but I thought I'd throw my 2 cents in just in case the other answers didn't solve your problem,

good luck,

jack
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Bad Blue, '86 245, 260,000 mi., Columbus, Ohio