I have a trailer northstar unit model# 66DX that looses pressure after you press the trigger. The pressue is great at first but dwindles from there. I have resealed the pump and replaced the spring valve what else could it be, I saw the solution about the different nozzles which i will try coulld it be that simple?

Most likely problem is that the unloader is bypassing water. As unloader wears it will by pass at lower pressure. Try lowering the pressure at the regulator to lowest setting then raise pressure a little at a time untill unloader releases then lower to prevent unloading. Using a slighly larger tip will do the same thing. Using a larger tip size lowers pressure.