i-600 backhoe - Hoe seems "stuck"?

Not that long ago, I bought my first machine, an older AC I-600 (from what I'm told), based on the D15 Series II tractor.  It has some issues I'd like to fix, and then sell it so I can buy my wife's grandmothers Ford tractor she is looking to sell.  Smaller, newer, like 700 hours, and parts everywhere are main benefits :)  Don't want to invest a ton of $ (bought for $3500 and put another $350-400 or so into it getting starter rebuilt, clean/rebuild/reassemble carb and completely replaced all ignition parts and upgraded to Pertronix), but don't want to have to sell it for $2500 or something because its not 100%.

1) Machine seems to be low on hydro power, and potentially getting worse?  When I got it, it would lift 1000lb hanging off the hook to say roughly 85% of lift height.  Obviously should go all the way up and I think its rated for like close to 3k.  It would go up a little more if I "bumped" the lever a little at a time... Hadn't done much with it for a few months, maybe only used handful of times.  Wanted to use again so before I did i checked fluid in the R arm looked low so I added some fluid (maybe too much, it was basically overflowing that plug after I added because I had hard time looking past funnel to check level), forget exactly which I had but think it was plain ISO 46 (it was red IIRC).  Then it struggled to lift to say like 30-40% of height.  Not sure if it was related to the fluid I added, or just was 1st time I used it since before?  Also - I assume this is not normal, but it also does not like to flip the bucket back up if it is fully dumped while arms are lifted.  I had assumed that was due to low fluid before, but that can't be the case now.  Not sure what to do, should I R&R all fluid, is there a screen/filter I should check/replace?  I do have a 3000psi pump from my snowplow work, i assume it would be good to try and get adapters and plumb this is somewhere, but not sure where?

2) The backhoe section that is closest to the tractor is giving me some issues, possibly both are intertwined.  When I park it, it leaks down and eventually bucket will come to rest on the ground.  Not end of the world, start it, pull it up to the tractor and away I go.  However, it doesn't appear I can do any actually digging with this at the moment because if, after pulling it up to the tractor, I try to push it away, it bogs the engine but doesn't move.  I presume it takes more hydro pressure to lift it up and push it away, so don't think #1 is (the only) factor.  Wondering if there is some junk/restriction somewhere between the valve body/junction block and that end of the piston?  Bucket and the further end of the hoe seem to go in both directions as they should.  What should I do here?  Not sure if it would be OK to pull off the hose from that end of fitting and make sure that when I pull lever fluid shoots out, and then look into that end of the piston and see if there is any blockage?  

Thanks for any and all suggestions!