97 Suburban sluggish (and sometimes "backfiring")

97 Suburban K1500 5.7L 120K: About 40% of the time, it starts sluggishly as though it is not getting enough fuel. Once started, it seems to run fine. A couple of times in the past 4 months it "died:"

-- Once by failing to respond when accelerating from a light (it stayed on and seemed to stay at idle even though the accelerator was being pressed). Shut it off, turned it back on and it was fine. Mechanic found no error codes.

-- Once by stalling as I put it in Park.

-- Last night it would not initially start but seemed to almost "backfire" and then a single puff of smoke came out from the hood. Opened it up, saw no visible signs of where the smoke came from, tried starting again and it started right up. This morning, no problems driving to work in rush hour traffic.

Any ideas would be very appreciated!