help!

i have a 92 gmc Z-71 with 220,000 miles. i just rebuilt the motor and am lucky to get 12 mpg on the highway. Recently it has become hard to start and drives eratically. When the truck shifts it bogs down if you press the throttle. Sometimes it feel like you flip a switch on and it takes off after bogging down. I replaced the fuel filter and it didnt help. I have recently replaced the regulator added accell wires, added a msd ignition, k & n filter, and a hypertech thermo master chip. I would appreciate any help I could get.

I'd start looking towards the catalytic converter.