Hello, I have a new-to-me 2000 Chevy Express 3500 Sportsmobile van with 98,000miles giving me fits of misfiring. It's been to 3 different mechanics in the last 2 months and the problem has not been solved. It started as an intermittent infrequent problem and progressed to be quite frequent--took it to mechanic 1 who replaced a faulty MAP sensor and MAF sensor. Misfiring came back shortly after. I took it back to that mechanic who checked connections and ran various tests and couldn't find anything obvious. Re-set computer, it drove well for about 100 miles before the misfiring returned. Took it to mechanic #2. Code P0175 was being shown and misfires were happening on all cylinders at random. He tested known good parts from another van and wasn't able to deduce any parts were bad on mine. He did replace the Crankshaft sensor--mostly because I was pressuring him to try something after 2 weeks of "looking". It didn't work. Still misfired and gave P0175 code. Took it to mechanic #3, and had him replace 02 sensors at advice from another mechanic I'd been talking with. Mechanic #3, also questioned why a tune-up had not been done and noticed some wear on a spark plug, so he replaced cap, plugs and whatever else with a tune-up. Still misfired. At my wits end I contemplated selling the van as I"d dropped about $2000 more than anticipated in repairs. Mechanic #2 found a new computer for $145 and I decided to take a gamble and have him install it. It drove excellent on 4 drives of about 10 miles, 2 drives of 20 miles, and a overnight trip of about 100 miles. No problems. I drove a couple hours yesterday and about 100 miles in, the misfire returned. The check engine light did not come on though. I continued to my destination with frequent misfiring. This morning I drove home, with very frequent misfiring unsure if I would make it and check engine light on. I don't understand why the new computer "fixed" it for awhile before having the same symptoms return. All 3 mechanics seemed uncertain of what to do, and I"m not sure where to turn next.