Howdy all, hope you had a good Thanksgiving weekend.

I'm looking for possible causes for a problem. The truck has a SBC350/TH350 combo. I've been messing with it to get it running right for the past few weeks, and I thought I had it. So I took it to work this morning(about 25 miles) it ran perfect for the first 15-18 miles then stumbling & missing from a standing start and up through the rpm's. After about 4 miles of this it started running good again. It did the same thing on the way home.

The motor: 350 4-bolt, 10:1, cast iron heads(2.02/1.60), rpm air gap intake, Edelbrock 1405 600cfm carb.
Ignition system: MSD pro billet mech adv distributor(set@ 10 idle,35@3200), Mallory HyFire VI-AL, Crane PS92 Ignition Coil.

Any ideas?