Don't worry that you have little fuel coming out of the return line if you have a plunger type injector pump. The return line is only there to deal with leakage past the plungers an injectors which is a small but significant amount. Say 1 to 2 % of fuel burnt.
N.B. There is a type of pump/governor which does bypass large %s of fuel but I don't think it is fitted to a 3GM.