I installed the new fuel pressure gauge sender today, and double checked the wiring on the gauge itself. Following installation of the new sender, the gauge reads 10psi with the pump on but engine off. After engine start, the gauge reads 9psi at idle. Driving on the flat and maintaining speed gauge reads 7psi. Pulling a grade with truck empty gauge drops to 5 psi. Pulling a grade and putting foot to floor drops pressure to 2psi. These results are in contrast to Laserjocks results in the first post. He is pulling a grade with a loaded truck, and has better fuel pressure (4psi) under load with the lower pressure pump (40222) and a modified truck than I do (2psi) with the higher pressure pump (40290) and a basically stock truck. I am still not sure what is going on here. The truck gives no indication that it is starving for fuel under load even though the fuel pressure gauge is (in my opinion) reading too low. The gauge needle still fluctuates while the truck is running but is it the gauge causing this, or is the pump just that erratic? Darned if I know. But a replacement gauge is not cheap, and just the new sender was $90.00, and I got a deal - usually the senders alone are around $125. I guess if I have time tomorrow, I will connect my mechanical fuel gauge. While I won't be able to see the fuel pressure under load, at least I will be able to see how it compare at idle.