When you're shooting hot, is it with Co2 or HPA? I've noticed Co2 shoots hotter than HPA.
To adjust the velocity by the springs you need to put either a "lighter" Hammer spring in or a "stronger" Valve spring in. I would suggest the first, it's just a lot easier, remove the front thumb screw pull the pump handle out a little, swap springs re-install the pump handle and thumb screw. If you want to put a regulator on I suggest using a Palmers Female Stabilizer, I mounted one on one of my Proline Sterling's and have had great success. If I need to drop the velocity I just turn the adjustment with a 3/16 allen key and get it all to be good. You'll see in the picture I just ran a macro-line fitting into the back of my "Donkey Body" you could just put one into the adapter on the back of your gun.
I hope this helps
Started with a Splatmaster, moved onto a Nelspot 007, then came the Autocockers, then a STERLING Pump, next was a Bob Long defiant then a PM7. As of now I have 10 Sterling Pumps, 2 Phantoms for SC, a CCM SS-25, a PGP and a Sovereign 3.