I have an LS4310 with 2500 hours. It has GST. This has been an unusual hay season [four full cuttings so far with at least one more to go]. Today I noticed that when cutting in 6th gear [clean up cutting, not for windrows] with heavy grass about a foot tall, the tractor would bog down when I went up a modest hill. Running at 2000rpm the engine would drop to 1500 and not recover until I either down shifted to 5th or got back on level ground. The problem doesn't show in 5th. I don't remember this from previous years. Maybe it is normal. I was racing rain, so I was asking the tractor and the cutter for all they had. It may be that I have not tried this in 6th before. Can't remember for sure.Anyone else have this experience or an opinion? Thank you for taking the time to help.