e30 hesitation when acceleration . idle fine

[tanner325ixx]

i have 1991 325ix and about 3 days ago my gas gauge started malfunctioning, going up and down and actuating erratically . then I felt a loss of power , and noticed my MPG gauge was really low . like in 4th gear at 2500rpms steady I was only getting 10-12 MPG I would usually get 20-25MPG . then today I was racing my buddy and when I punched it it started bogging , kind of sounded like a rev limiter , but more like a hesitsation .
i replaced the sending units and that fixed the wacky gas gauge . and i put in a used pump . no idea if it was good or not , but when i ran it it did the same thing . fine at idle , then when i got on it a little it hessitated for a couople secconds then accelerated , and it repeted that for the entirety of the drive
it was cold when i took it for the seccond drive . not sure if that would make a difference .
PLEASE HELP ME , Any imput is good :(:(:(:(:(

[ahlem]

Check fuel pressure. Be sure your grounds and connectors are good and clean especially on fuel supply related components. Then check hoses for vacuum leaks. Sounds like a fuel supply issue from way over here.

[Psygo]

I'm actually having the same problem with my 1988 e30 m30 swap, but it's using the m20 harness so it's basically just a regular e30 when it comes to that, and it blows fuse number 9 constantly too, haven't gotten around to looking at it though.

I left the car for 10 days a little bit ago for vacation and it started doing this.