Sorry to alarm you Pepino - I thought you were getting 150 miles per tank regularly. 260 miles per tank is about right if you drive hard on oxygenated (10% ethanol) gas like I do.

If you don't know your way around an engine, then changing the FPR is no place to start learning. Any mechanic should be able to take care of it for you - an hour's labor to install it plus the part, which you could get at an Isuzu dealer, online, or from an AutoZone or other parts store. It may help, it may not.