'06 Hummer H1 alpha, lly, stalling issues
 

I have an '06 alpha hummer with lly engine. truck started stumbling at 60 mph, then stalling. by time i go it to dealer it was generally just stalling out, restarting, going couple of hundred feet, then eventually wouldn't go, towed it in. At the time no codes were thrown, later the maf threw codes
dealer had truck for nearly two months, here's what they did. Replaced MAF (siad it was throwing codes, nothing to do with stalling). Dealer found air in fuel, found a line with hole, replaced line & fuel filter. Got truck back for 1/2 day, same issue, except i was able to drive it back without stalling. Dealer then says beileves tank is dirty, drop tank, tell me that the fuel pickup is basically clogged, recommend tank flush. They do this, truck is still having same issues. Dealer tells me that the predator ecu is corroded and thats causing the stalling. i go look at the ecu, ZERO corrosion. I say fuck it, pick up truck, thisng runs worse than when I picked it up secind time, have to tow it home.
I put a gauge on the fuel port, got 2' of vaccuma at idle, went up to 5' at 3K rpm's. Don't know much about diesels, not sure how to interpret this.
Looking for direction on where to look next?

Frank