Legacy Gt 1990 Problem

Hi guys i own a 1990 legacy gt sedan
and of late i have had a few problems with the ca just stalling in traffic
and loss of accleration .

For eg Idles fine no problem put your foot down and she goes
hard as but just crusing along all of a sudden u will loose power the revs drop right down and she stalls .

Starts fine again and she idles fine go to drive of put the foot down and she goes like a rocket and then crusing to get back home and all of a sudden
power loss and the rev's drop down and she stall's .

Now i have a feeling that it might be the fuel i have out in it
because the servo where i got the fuel from was all out
of premium unleaded so i said ill put $ 5 worth of unleaded only
just so i can get to the next servo which had premium unleaded
.

Now as i have run the car so low on fuel could this have dragged somthing up through filter and is causing a blockage ?

or has some one else had the same problem as me ?