1982 Chevey C-10 6.2L
 

Hello All, New to forum and I surge problem. Get to 35mph and truck will start to surge, can get upwards of 45 but afraid to take on highway. Replaced primary and secondary filters, and mechanical fuel lift pump. Bled system starts still surges. Could use some suggestions on waht to do next. Thanks in advance --BJG

I would start by replacing the IP fuel return line with clear diesel rated fuel line(tygon) and idle the engine watching for bubbles,bubbles indicate air intrusion in the fuel system.

Normally the air enters between the fuel level in th tank and the LP.

If bubbles are present,the hole in the line needs sought out and repaired.