If anyone can help before I pull out all my hair. I have a '99 burb, 5.7 - intake was leaking (big surprise).
I replace intake gasket, ran great (major pat on back), two days later surging - skipping - missing at all speeds.
When I replaced the gasket I also changed plugs, plug wires, cap and rotor.
Tried some remedies listed here, Seafoam and such.
My mechanic drove it and suggested updating the fuel injection spider, so I did.
Ran great for 2 days, now same problem. I have read about fuel pump, egr and distributor but I didn't have a problem before.
I would greatly appreciate any suggestions.

Welcome to AF. Start with checking the fuel pressure, look for 60-65 at the rail.

As Max said, fuel press is #1 to check. I've not done a 5.7 but I assume the dist has to come out for the gasket change. That would be the 2nd thing I would check. Need a scan tool that can access "cam retard or cam offset".

When in this mode timing needs to be set at 0 +/- 2 degs with eng rpm's at or above 1000.

Welcome THDH. I feel your pain I have the same vehicle same repair and it started missing. Mine misses in higher gears especially when towing and when wet outside. When you find out what it is please advise.

Thanks for the great advise, over the past couple of days I have noticed the problem is only when raining, possibly when towing but I haven't had the opportunity to try.

With moisture being a clue, wouldn't that be distributor?

Well after mucking around a bit, I finally got a SES light.
The ETC sensor was showing -40F and spiking to 200F, put one on and so far so good. Everything seems fine for now.

"thadh". Thank you for the post back on what fixed your troubles. Something new learned for me and hopefully a bunch of others...........Steve