4610 hydrostat issue

Hi, I'm a newby to the forum.

My tractor is a JD 4610 with a hydrostatic drive. My problem is when going forward in any gear(A,B,C) with the 4 wd in or out the tractor bogs down to close to stalling, so I let up. Works great in reverse. Flat level ground in both directions.

Can brakes drag in one direction only or do I have some other problem?

Thanks
D McCoy