I have a 5.9 cummins and when I pull my trailer up a hill i put the pedal to the medal and nothing happens. The rpms stay flat and I lose power. If I take my foot off the gas then kick it back down then it will kick in and drive up the hill. I use to be able to pass someone going up a hill. Doses anyone have any ideas what it could be ?

 

I'm thinking your throttle position sensor or something isn't picking up the fact you've depressed your skinny pedal.

I don't think I've ever had to 'floor' my throttle in my 5.9... Put it down another 1/4" to 1/2" and away she goes.

 

I have had a few people tell me it might be a lift pump but there is no way to check. Any ideas how I can test if lift pump and what are your thoughts ?

 

Change your fuel filter

 

I changed the fuel filter last week and didn't make any difference. I still lose power when going up a hill.

 

unless you have a fuel pressure tester handy and the adapters to hook it up your sol..the lift pump will cause it to stumble at WOT and can cause hard starting also