85ta4bm

ok i have a 85 t/a 350 tpi, just got done replacing my heads (just got them rebuilt) it ran alright for a couple of days, the first day i drove it to work 8mi the highest my new temp gauge read was 200 the lowest was 190, bout 50 degree weather when i got off and went bout 20miles the highest was 230 but in stop and go it was around 210 (is that normal???) anyways when i got home and shut her off i heard a kinda soft pop!. today i drove bout 25miles when i got to my sisters house i reved it up before i turned her off and pow (the whole neighborhood heard me) after bout an hour i started her up she ran fine for a minute then a rough (searching idle) while in drive (did that before but a lttle rough like it was going to stall out, but didn't) in neutral a little better but not perfect that's only when warmed up, cold she runs good. My Q is why did it backfire only when i shut it off, other than that it ran good while accelerating no power lose...

these are the things i replaced while doing my rebuild.
cap, coil, rotor, module, spark plugs (hedder plugs) wires, fuel injectors (svo) cts, water pump, upper and lower radiator hoses, rockers, rods and lifters, AFPR(BBK) to match my color scheme, i couple of other thing i can't think of right now. my tps is at .55 and i cleaned my IAC out.

the only thing i noticed is my oil psi is a little low when it's warm, around 15 psi when in idle and about 30-40 when driving (going to get a new oil pressure sending unit tommorrow) when i first start it it's around 40 psi. What kind of oil should i use 10w-30??? that's all i can think of right now. Any answers would be greatly appreciated, or if there is anybody around youngstown ohio that could help me out that would be great...