My F3680 bogs down (if you drove the mower into thick, tall grass too fast) and I can not figure out why. I had a problem with the left rear bevel gear box - a couple of the bearings had disintegrated - so I thought it was a matter of the gears binding and "dragging" the mower down. I have replaced all of the bevel gear case parts and all of the tires/wheels spin freely with no oil leaks. When I took it out of the shop to drive it around after repairing the bevel gear box it still bogged down. I am hoping someone can give me areas to look at before I give up and take it to the dealer which will cost me big buxx to fix. Any advice would be appreciated.