04 996tt, until today fuel gauge slow to react to filled tank. Level eventually dropped to just under 1/4 tank. Threw $25 in fuel at it and gauge registers under 1/4 tank, fuel level warning script lights up. Fuel sender or gauge failure? Any way to test this? Any direction would be greatly appreciated.

 

Same issue but until I either get a good direction or send to the shop I'll keep more than half tank in it