i got a 91 4.3 s10 4x4 i was hauling home one night and had it pinned at bout 4 grand for bout 6 miles was doing ovr a hundred then i stopped for stop sign i started acelerating easy and all of a sudden it started hitting and missing big like it would die and then go. the tach was jumping all over thot it might be dirty air filter wasent. changed ditributor rotar and plug wires but not plugs figured it woodnt b plugs cuz it idles great and it will only hit and mis when in over drive or acelerating hard. it was also running rlly rich i cood smell rich gas bing burned from exaust. my dads 90 suburban is doing the same thing and we r both stumped could it be the computer is messed up and not mixing the rite fuel to air ratios thev never been touched everything stock

 

No engine lights getting set off is there

 

Sounds like you really pissed it off going triple digits! LOL

 

no engine light coming on kinda weird i switched the map sensor and didnt help made observation today it ONLY does it in over drive if i put it in reg drive it will do it very rarely and only a couple times then runs fine i have been noticing it missing a litle in idle but u can barely tell im gonna run a dignostics

 

Does it run properly if you disconnect the O2 sensor?

 

dissconected the o2 sensor today didnt help anything

 

I had the same problem with my 94 (w) blazer!! after months of pulling my hair out I found the problem. Well I turned out to be the connector on top of the cpi. After being taken off so many times (264.000 mi prob 3 or 4 cpi's) and all the carbon under the plenum the terminals in the connector were making poor contact on the cpi when the engine got hot. How I found this was with the engine running and hot I lightly pulled on the blue and red wires that go through the lower intake manifold to the cpi and the engine would stall! So I pulled the plenum off and carefully took apart the connector and cleaned and lightly squeezed the terminals to make a tighter contact around the studs on the cpi. That was over 2 years ago and the truck has ran fine since! Hope this helps.

Oh this also first started for me after a long WOT on the PA turnpike lol

 

i figured it out it was dirty injectors coupled with bad spark plugs it also had a vacum leak but yes i pulled my hair as well but now it runs like a champ

 

glad to hear you got 'er fixed.

but brother, you really need to punctuate your posts! it's sooooooo difficult reading run on sentences.

 

lol u sound like my english teacher