Sounds like you got it running but I would think that you should be getting more fps. My tuned.177 RWS34 Panther is pushing the 8.6 FTS @ 870fps and the 7.9 CHP's are close to 900fps. Before the tune the shooter was getting tired but still pushing lead at 840fps. Ed
You may have to let the seal break in. My M34P shot slower to start then picked up after about 2 hundred shots. Also I had used too much grease and it was messing up the velocity, once I cleaned it out it jumped up to a respectable speed. Also did you leave one washer in the piston? If not you may to go back in and put one in there.