Lift arm drop on 3720

[Dex]

I need some information for my tractor. I have an 05 3720 with a 300x loader. My problem is that my bucket drops without activity to the tune of about 4" per 1/2 hour. Noone else around here is having that problem. This all started after I had my top and tilt installed. I need some horse power since I had my tractor at the dealer for the past 30 days and they said all was fixed and well. I brought it home and it dropped just as it was not worked on. They replaced the silonoid and valve for the diverter. They even replaced the main spool for the T&T/loader. Any advice would be appreciated so I can get this thing fixed right.