Where is the air leak?

[cluckmaster]

Hi.. Just joined this weekend, and I am having a problem fiding an air leak (I think). I have a '97 4x4 w/ 120,000 on the motor and 220,000 on the truck. Only mods are straight piped exhaust, Amsoil air filter, removed silencer ring, and a #8 plate that I installed recently, and haven't had a chance to tune yet. Truck started stalling about 10 seconds after starting up, and then I'd have to crank it for a while to get it going again, it would run rough as hell for twenty or thirty seconds, blow tons of white smoke, then smooth out. Dad and I replaced the lift pump and the problem is still there. Checked the check valve on the return line off the pump, and the spring is still good. We pressurized the tank and searched for leaks, and can't find any. We can bleed the lines and crank it for a couple seconds and it will start up, then tighten them back and it runs smooth. It will then run good until I let it set for any length of time, so I guess the fuel is draining back out of the system. The fuel shutoff solenoid is working, both the pull in coil, and the hold coil. We are about to try just replacing the fuel lines, but the fuel lines go from metal to rubber covered w/ wire mesh at front of the cab, and they are joined by a compression fitting. Any ideas on how to replace these? Also, I keep reading that the return line is often the culprit, but how does air get into the system from the return line? Does the return line go to the bottom of the tank to deposit fuel? Any suggestions on what the problem is would be greatly appreciated. Thanks.