Hydro issue

[Wayne h]

Hi everyone new member on here. I am hoping someone can help me.I have 2004 jd 4410 with hydrostatic transmission when going forward the transmission surges like it is kicking in and out of gear but it doesn稚 do it in reverse. I have changed the fluid ,filters and cleaned suction screen with no change in performance. Wondering if anyone has encountered this issue and give me an idea how to fix it. Thanks