Popping out of intake and exhaust!

[lt1truck]

I just got my ltx swap running on its own but i ran into a problem. Right as i got it to run on its own it ran good, it had good throttle response, no smoke and no codes granted i never had coolant in it nor ran it long enough for it to matter.

When i set up the cooling system and got it all burped i let it idle there for about twenty minutes and thats when the issues started. it started to pop or backfire out of the intake and exhaust when i brought it off idle but once it was up in the 3500-4000 rpm range it would get very responsive and sound good, i also pulled some of the spark plugs out and they looked fouled out. issue two: after i noticed that i shut it down and started checking over everything obvious, and when i checked the oil it smelled heavily like gas and i could also tell by the feel of it. so i obviously have more than one problem here.

I have already tested all the injectors, i pulled vacuum on the FPR and it held good vacuum, new plugs (because the ones in there were questionable to begin with), checked for vacuum leaks, i had none, tomorrow im going to do a compression test and check my fuel pressure. Anything else anybody can think of i would be happy to listen!!