Stalling problem

i just got 87 astro with 4.3L engine. I cleaned under the hood area with GUNK degreaser. Since then i am having stallling problem with my van.
It idles smooth though, never stalls on slow speeds. but between 50 and 60 kmph it stalls and engien turns off compeletly. Over 60 engine turns off and "service engine light" comes on but if i pump the gas pedal the engine turns back on right away. I have cleaned and dried(with a hair dryer) all electrical parts and wires, distributor caps etc, still no help.
Please advice.......................................