I have a Ford L9000 dump truck that I recently replace the pop off valve on bottom of air dryer since it wasn't completely closing and leaking air constantly and causing loose of air pressure. Now I have a new problem with it. When going down road and I'm in the accelerator it is constantly popping off like every 10 seconds (sometimes a slow spit/hiss unlike when it was working normally with one hard release of air pressure), but I still maintain air pressure around 123psi the whole time. When I let off accelerator the air slows down or stops. When I'm sitting still at idle it will sometimes still be slowly letting air out but when I first start up truck in the morning it will not let any air out at all. Like I said the pop off valve on the bottom of the air dryer is maybe 3 months old. Any ideas?