Fresh TBI swap onto a internally stock, Vortec-headed 350.

Truck runs great, pulls great, sounds great, except for a hesitation/TB back fire when going from idle to WOT. Also, sometimes from part throttle to WOT (like from turning a corner, then flooring it). Sometimes it's a single "pop", then it takes off. Other times, its a series of "pops" and I have to get off the pedal before it will recover. I've been playing with the base timing (yes...bypass was unplugged each time). Started at 0° and up to about 6°. As you might expect, it gets worse with more advance. It gets better at 0°, but still does it. No stored trouble codes, other than code 42 that I never cleared after unplugging the bypass.

I've got it locked down at 0° for now. Haven't spent much time troubleshooting it. Just got the truck running Friday, trans dialed in Saturday, and started playing with this issue today. I'm out of town all week for work. Just looking for ideas and things to check when I get home next weekend.