Hesitation Problem, need help!!!

I got a 87 B2000, Stock everything! except suspension.

when i drive at a steady pace, in any gear. Between 2200RPM and

2500RPM. My truck starts to hesitate/bogg down. I ALREADY replaced the

EGR vavle, fuel filter, fuel pump, got a tune up before i had to SMOG it

(barely passed).

Im stumped because i dont have anyother ideas what else it maybe.

Any suggestion would help .

does it do it when you just sit and rev it up?

timing advance is slightly off

If i rev it inbetween those RPMs, it kind does it. but its worst when i drive it and ill have my timing checked again but it did it before and after i got my tune up.

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yes! i hadda clogged cat that was making my truck run all kinds of funky once...