I'd try swapping springs. Some people throw low pressure valves in there and leave the stock springs. The stock valve spring is just too heavy and will close the valve before enough air has gone through (spring pressure closes the valve, air pressure just keeps it closed). You probably want to start with a yellow valve spring (the lightest one in most spring kits) or possibly a green one (second lightest) if the gun's still set up to use Sheridan springs (I think stock '97 'Cockers still were, but someone may have switched to nelson springs along the way). You might have to change up the mainspring as well to find the right balance.
Once the valve spring is lightened up, you should be able to drop the input pressure and see an increase in velocity. Basically, set the rear velocity adjuster all the way out, then lower the input pressure until the velocity peaks (as you go lower, it'll top out and then start going back down - turn the adjuster 1 full turn at a time and make sure you take at least 5-10 shots at each adjustment to let the pressure normalize) - when you find the pressure where the velocity tops out, that's your "sweet spot" - DON'T adjust the reg any more. Go back to the rear vel. adj. and you should be able to dial it in to get a decent velocity. If not, then try a heavier mainspring. Also, adjusting the input pressure will probably require tweaking your LPR (if it's externally adjustable - if it's not, you should be fine).