After using the brakes frequently like parking or backing a trailer up the pedal gets very hard to push and does not stop the truck. Any ideas would be great

 

My first guess would be the vacuum pump, but I am sure someone else will chime in soon.

 

My truck has always done that. If you pump the pedal too many times you use up all the stored vacuum, and braking is very hard. Rev up the engine a bit to 1500 or so, and you can pump up some vacuum a little more quickly.
-Del

 

I dont know about you guys but my truck uses hydroboost power via the power steering pump for the brakes and not the vacuum pump, which is used only for the HVAC vents in the cab. I would think your guys trucks would be the same, just look behind your master cylinder, see if there is a hydrobooster there or a vacuum booster.

 

'94-'96 use vacuum boost and it is totally normal to use up all the vacuum by braking several times while idling. Either high idle it or add a vacuum reservoir to correct this problem