sounds like not getting enough fuel, do you have a black washer inside the truck half of the LPG tank quick disconnect?
you say the truck ran for 4 days? did it run -correctly- for 4 days? if so, I would not blame the install. I would expect something after the install.
you say it "bogs down about every 2 minutes" how long does it "bog down"? does it come right back or stay "bogged down"? does is do it just sitting, or only when driving, or when lifting but not moving forward or reverse?
Have you confirmed the transmission speed sensor is connected? is there any possibility that the VCM or ECM was swapped with another truck while it sat? (installing a pnuematic's vcm into a cushion truck, and/or installing a 3k vcm into a 5k truck makes symptoms somewhat like that, since it has a different number of counts in the trans sensor for different engine speeds, even if the truck is not set to have speed control)