this system is a conversion kit from street & performance from out of arkansas, on a '95 LT1/700R4 combo in a 55 chevy. [i was a little hesitant to mention this at first; sorry] it uses a reprogramed computer [done by them] from a "??" camero [if i remember correctly]. when originally installed [and this was the first and only time i have dealt with a fuel injection conversion], there were many back and forth phone calls between myself, the car owner [who is no first grader when it comes to fab and electrical work on vehicles], and "mark" [the owner]. with the help of a FSM from a 96 cadillac, which has a very good wiring diagram section, as well as a diagnostic section, the conversion was a success, and this thing ran GREAT, plus got EXCELLENT gas mileage at around 27mpg. everything was going good for many years until last fall when the symptom started. the first thing checked was for vacuum leaks. none were found. next up was the IAC motor, which was first taken off to see if the pintal was stuck or carboned up. that looked good, so it was then given a 5v signal while watching it step up and down. that looked good, so using the FSM, it was returned to the length needed to re-install. nothing was improved, so on to the TPS. first, my [old] OTC scan tool was used to watch the action from idle to WOT with the engine off. that checked out, so it was monitored going down the road, and it worked as it should voltage wise, but at 1800rpm or above, it still went into "cruise", but lower than that, it acted as it should. next, we checked everything else we could think of, with nothing helping us out for a cure. the FSM doesn't have anything describing this particular malady, so we were stuck. calling street and performance, we were told "mark" had passed away, and "james" was now the man in charge. he suggested sending in the computer to be checked, and to see if the symptom could be duplicated. we sent it in, paid the diagnostic fee, but nothing was found. the setup was re-installed, but nothing changed. still goes into "cruise" when letting off the throttle at 1800 or above, but when sitting still, rev to the moon and will return as it should every time. the only thing not checked to this time was the VSS on the transmission. speed and performance will sell us one [it's an 8K or 4K per mile unit - i would have to look] for $100, but couldn't tell us how to check it [ohm reading or otherwise.], and going by the caddy FSM, this may not be able to be done because of the modified computer. "james" doesn't seem as curious as "mark" was in trying to work with us, so we are at a stand still. we tried unhooking various sensors [but i forget, as we have done so many things] and driving the car. some made no difference, some, the car didn't run worth a hoot. i guess we will have to start over, recording what we do and what the results are, so we have a record. diagnosing a problem instead of throwing parts at it is how both of us [the owner of the car and myself] think. we just need some direction in how to proceed at this point. sorry this has turned into such a long drawn out deal.