98 Rodeo gas milage problems

Well I just rolled over my 98 Rodeo (3.2 V6) to 200000 and all of a sudden it gives me funky gas mileage/readings. In the old days the gas light would come on and I could put around 16-17 gallons in to fill it
back up but now when it comes on I can only put in around 12 before it fills back up. I can top it off and drive for about 45 miles and I'm already at 3/4's of a tank. I've been afraid to test the actual tank levels for fear of running out of gas, but the actual mileage seems to be slightly worse but not enough to cause the discrepancy. I keep it tuned and change the oil on a regular basis... but I'm not enough of a mechanic to try to figure out what might be wrong. So I thought I'd check in here first to make sure it wasn't something simple that I could repair before I take it to the dealer. Any ideas?
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You may have backed over something and dented the gas tank, which would reduce the volume in the tank available for fuel... My brother did that in a Jeep once.

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Thanks for the tip, I hadn't though of that! But unfortunately (or fortunately depending on how you look at it) there was no dent in the gas tank.

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I have 98 Rodeo as well. Not nearly so many miles, though. Dang! From the start, the gauge was a little iffy. Did a little research, and found that this is a common problem for this model/year. Isuzu is aware, but there is no fix or TSP for it. I do exactly what you probably do--get to 300 miles on the 21+ gallon tank, then fill it up (usu 17.9 gallons or so) and reset the tripometer. Regarding a sudden change in this, maybe just the gauge has deteriorated to a new and even worse level? Are you still getting the same actual miles per gallon, just the behaviour of the gauge has changed? Definitely odd, but too pricey and hit-and-miss to drop the tank and have the sending unit replaced. Maybe just keep charting your miles and ignore the gas light when it comes on.
sinner

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