The tachometer and fuel guage, specifically.

The tach works sporadically. Sometimes works, sometimes just sits there dead. Totally random.

The fuel guage is generally pegged at F. Occasionally it'll drop to 3/4 or half a tank at random, but usually stays at full no matter what the actual fuel level is. We've just been filling the tank when the trip odo hits 300 miles.

I'm not really sure what to make of this. Any thoughts? Everything else works just fine. All I've really done so far is check the fuses.

Well there are two possiblities i can come up with. One, it could be that contacts on the back of the cluster need cleaned. There is a techinfo article on cleaning bonneville clusters. Or two, the contacts on the back of the cluster need cleaned, and coincidentally the fuel tank sending unit is also bad and needs replaced.

ok so heres more of an "your're not the only one" answer...

my pop'* 97 Limited had this issue. the car had 50,000 miles..

We went to the dealer and they gave us a brand new cluster. Our gas gauge was never accurate, infact before GM replaced the whole unit, their service guys reversed the connection for the gas, and it was always on E. This was what they did to see if the connections just needed to be cleaned, however sometimes odometers cant be fixed and need replacement. Believe me i remember those days, not fun.

Does your speed needle sometimes not work correctly? How many miles are on the car? I would also check out the Fuel tank sending unit. Im no expert on that, but it makes logical sense.
Goodluck
pete

FYI - my sister inherited the car and to this day the cars run perfect besides that issue.

The car'* got 160,000 miles and everything else in the dash works perfectly. It'* just the gas and tach dials.