So I have swapped all 93 wiring harnesses and the dash from a RC into my 74 PW with an in cab fuel tank. The gauge initially read 3/4 tank when I turned the key on and didn't fluctuate at all. But when I drove it the gauge fluctuated about 1/4 tank consistently, the roads are really crappy here. It didn't do this before the swap and my 92 doesn't do it either. I made two 24 mile round trips with the truck, then on it's third trip the gauge was fluctuating down to a 1/4 tank so I figured I better fill it up to be safe. I put 27 gallons in what is supposedly a 24 gallon tank so I'm thinking it was about empty. I know the resistance values for the senders are the same.

So my question is, is there a mismatch here I'm not aware of between the gauge type and the sender and is there anything I can do to correct it or compensate for it?

I am pretty sure there is a difference in the sending unit values. Just like you saw with the temperature gauge sender.

These work great. Meter Match

I have one, I don't know that great is the word I would use. More like what the OP is seeing is what I have seen from my Meter Match.

Then you have something else wrong. If both your gauge and sender can make the complete sweep the meter match will work GREAT. If you have any glitches in either the sender or gauge then it will not.

Except that it doesn't.

New gauge, good sender (double checked with my Fluke), calibrated properly Doesn't work properly. It's consistent in how it reads, it just doesn't read right. I might try to recalibrate it when my son is here.

I would try to re-calibrate it. Some how your settings must be inputted wrong. Make sure your battery is fully charged. What I found is it took a few minutes for the gauge to settle with each push of the button. I started with an empty tank. I then added 3 gallons and set the e/low fuel setting and then I filled the tank and set the f/high level. I did not use any of the other available features. My gauge works better than what it came new from the factory. Several other friends have used it with the same results.

You may be on to something, I didn't wait long enough is most likely the issue, working alone, MM is mounted in the trunk so I had to eyeball the gauge thru the back window. Did similar to you, ran the tank dry added two gallons and calibrated empty. I did run thru the 1/4 and 3/4 tank options then full. I will do it again. Thanks

You are correct, about a 20 ohm difference at empty 90 + - with 93 and 73 ohms with the 74. Full is within one or two ohms. So the lower ohm reading with the 74 unit would show higher on the gauge. I put a 100uf capacitor on the signal wire and that cut the fluctuation down on the gauge about half.
Thanks for the info on the Meter Match, I'll have to order one.

So I got the Meter Match yesterday, installed it today. I removed the sender to calibrate it. Even though there is about 2/3 of a tank of fuel in the truck the gauge still read full after calibrating full and empty. So I did the mid high and mid low calibration at about 2/3 and 1/3 respectively. It now reads about 2/3 of a tank where it looks like it should be. I sweeped the float and the gauge appears to be working pretty good. It still moves a little just sitting still, but that could be my sender. I think it is original to the truck I guess I'll see how it goes. I also had to do the voltage limit function as I calibrated every thing just key on. With it running the gauge read half way so that would have been off. Thanks again for the help.