85' 4000 coughing at 4K rpm's

[Derick Farfan <bg18461@binghamton.edu>]

I am have notice now with my 85' 4000S(fwd), that when i am in first
gear, as i accelerate when the rpm hit about 3500 the car jerks
violently back in forth until i let off the gas.  To get up to speed, i
will have to slowly accelerate up there and even then i still get a
faint jerk.  This also happens in 2nd, but not as pronounced, as well as
3rd, but by the time i am in fourth it is fine.  My fuel pump is about
to go as i am hearing it whine again, (changed it last summer:().  Could
this problem be directly related to the fuel pump or is it something
else.  I had the timing adjusted, i previously had it advanced a little
and i wsa running on 93 octane, (what a difference). But my friend
borrowed the car one evening and filled it up with regular.  The engine
began pinging soon after.  So i had to adjust the timing back to its
normal position, but she hasn't been running the same since.
TIA