The truck is an 1989 K30 with the 454 TBI. It seems to run pretty well, but recently the gas mileage has gone from about 8-9 to around 4 mpg. It also has the following problems or symptoms: At cruising speed on the highway it seems to cough or lose power causing a bucking sometimes. It doesn't have the power going up hills that I would think a big block truck should have. It does not have enough power to stay in the top gear of the TH400 on a decent highway grade. It will slow down until it shifts. I would think the stock 454 should be able to pull a grade at speed with 4:11 gears. I have seen the check engine light on once or twice for a minute or so, then it when out. From time to time, I am getting a sulfer smell out of the cat. When starting warm sometimes it will die and be hard to start. Seems like a vapor lock, but the elec. fuel pump shouldn't allow that right? Anyway, I have replaced fuel filters and replaced the O2 sensor. Some one suggested TPS next or the MAP. I have also heard the cat could be clogged. It was taken to the chevy garage 6 months ago (when the gas mileage was still good, but the power still sucked) and they said the power problem was the transmission. I think that was BS. Anyway, I am guessing the computer is not throwing codes, or the check engine light would be on full time? The plugs do not look fouled. The actually look like the A/F ratio is pretty right on. What do you guys think the next step should be?