I have a 1991 Silverado with the 5.7 TBI engine. I have Tuner Pro RT and have logged a few (one for sure, not sure what happened to the other) data streams while driving. Generally things seem about as expected except that whenever my throttle opening gets up near 50% my vacuum goes to zero. Maybe that's normal but it seems to drastic. Idle vacuum is good, transmission shift points seem about right. Overall the truck seems like it is dragging an anchor and fuel economy stinks (10 mpg empty, 8 towing a trailer). Transmission will unlock with just about any throttle or load input, and it will downshift out of OD to maintain 70 mph empty (worse with the trailer).
Any thoughts appreciated.