Two items on my Ford Truck, fuel gauge and low power of engine

[lake side bob]

Fuel gauge: Started acting up Tuesday. Driving down the road and the fuel gauge dial moves to the left side various locations between 1/2 and "E" empty side of the circle dial, with the two Ford 50 gallon fuel tanks full. Why would that be. I came to a stop sign and the fuel gauge then showed full, this has been happening the last few days. I can not think of what could be wrong any ideas? What to look at.
Engine Power low; I noticed the engine power was less then normal so I changed the fuel water separator filter a couple hundred miles ago. No difference in power, any suggestions as to what to look at.
The power reduction is noticeable going up a hill and getting up to highway speed on the flat land, loaded and empty.
1992 Ford FT900, it is a nice truck but could use more power like another 100 HP.
vin 1FDYL90A7NVA28052
Used to get 7.34 to 7.97 miles per gallon now its around 6.33 mpg
miles on engine 163,000
engine is Ford 7.8 L 225 HP
Bosch injection pump P3000
has Bendix air dryer changed out cartridge 1,321 miles ago

 

[Coaldust]

Ground the fuel sensor wire and see if the gauge pegs full. If it does, the gauge is probably good. Remove the sending units and test them with an ohmmeter.

 

[Mike L]

Check the air filter. Is it turbocharged? If so check turbo and check for boost leaks.

 

[lake side bob]

Well the mechanic looked at it and found a hole (can put your finger through it) in the hose on the pressure side of the air rubber hose into the engine.
Now how did that happen.

 

[mks]

Four legged pest?
Look for grooves around the hole.
Changed two spark plug wires on a van cut through by something with teeth sharp enough to leave grooves.