bucking and stalling

[fixkick]

Hello to all, New Guy Here,
 I have a 93 Geo tracker 8V 3 speed w/120,000 mi
some time ago my truck started to buck at cruising speed so i replaced the fuel pressure regulator. This did not make a difference so i got use to it. Then the truck started to stall for no apparent reason just going down the road???  This happens periodically, I put it in neutral  and coast to the shoulder. The truck would continue to idle around 600 rpm but if  accelerated, it stalls? After turning the ignition off and back on the truck starts up and runs great (except for the bucking) until a random amount of time when it will do it again. so where should I look next as i know that the next time it may not start again. 
Thanks for any help 
 Douginhull

random bucking,
Does the check engine light glows?, key on  every time?, then goes out running and stays out running but if the engine stalls, CEL goes go back on, sure. back to key on only state.
so at the stall, right foot can not save the stall?
the engine ever get a full tune up the last 60,000 milles? spark parts all new? plugs/wires/cap/rotor?  (got excess miles on the cam belt 60k is spec)?
check the front large 17mm crank pulley bolt set to 94ft/lbs.  if not kiss of the crank front snout key damage there.

600 rpm most times means the EGR main valve is suck open  it must be clean or it sticks or replaced.
if fuel pressure is ok then the pump is ok.  but low fuel pressure cases bogging not bucking, bucking Implies gross spark loss, (spark loss is the most violent of events not fuel starvation)

to witness how fuel pressure acts, pull the fuse marked,  FI  ,  while parked and running,,this kills the fuel pump and see how the throttle acts , it bogs and slows and dies.

spark  can fail for lots of reasons on old cars, not just the above.
drive with the DTC   diagnostic jumper in place, when it bucks the the code 12 (normal good) changes to 41, or 42,  then BINGO you know why.

a bad ECU can also do this , the infamous bad caps  caused.  easy fix for $5 and soldering pencil
other causes the spark coil connections rusty and distributor side plug rusty (corroded) 
all the ground to the ECU , bad? rusty,  seen under hood fire wall, bolts distrib ground wire lug loose. seen here?  https://fixkick.com/Good_Bad_Ugly/common-failures.html


when the engine bucks or stalls do you lose power 12vdc to the cluster in any way?  gauges drop dead, or the like? (radio does, head lamps dim, all things electric act up?)