1976 IH front loader lifts to slow. With no power

i have a 1976 IH 2500 series b front loader with backhoe. Since i can remember the backhoe has always run out of power after about 30 minutes of use. Which was never to big a deal because i didnt use it much. However the front loader has always been extremly strong until recently. A couple weeks ago i got my tractor stuck in a swamp and thanks to my luck I blew the main line that feeds the backhoe from under the middle of the tractor. when it blew i was using the backhoe landing lift arms to pick up the tractor from the mud and add logs under the tires to drive it out. But in the process the line blew and i lost a ton of hydraulic fluid. so i had to change the line in the swamp. After the new line was installed i added approx 8 gallons of hydraulic fluid and drove my IH out of the swamp under its own power. But since that day my backhoe has gotten worse to the point i cant even use it and worst of all the front loader wont lift or curl unless i throttle up the rpm's. I have tried to bleed the system but it doesnt help. i am not sure if im doing it right. But i cant seem to find a procedure to bleed the tractors hydraulic system. My other thought is maybe i drained the system and reservoir so low that any contamination that was in the system got sucked into the pump and now i dont have good fluid flow??? Please Help. i need my tractor running strong like bull again. Too much work to do with it. but the hydraulics are killing me. thanks for listening. :x

All though I'm not totally familiar with your tractor. I think their are 2 hydraulic filters on your tractor, one under each floor board. If you have not changed them, that's where I would start. Their should be 2 drain plugs, one in each housing of the transmission and rear end. I think the one on the right side is for the hydraulics, but in any case check both filters.
PS: Have several buckets as their is more than 10 gals of oil in each housing.