Bicycle Mechanics - Any way I can get more chain tension out of my RD?

I recently got done building up an old Stumpjumper with lots of NOS parts. The one giving me trouble is the Deore LX rear derailer, circa 1994. The problem is that it doesn't tension the chain enough. Every time I go over a bump the chain is slapping the chainstay. It's really annoying offroad. I will probably get a chainstay protector, but the chain is still way too loose for my liking. None of my other bikes have this problem.

Is there anything I can do to the springs to make them pull more? When I cut the chain I did big/big +1. Can I take a link out and just never use the big/big combo?

Thanks.

when you pull the cage forward [towards the crankset] how does the tension feel compared to one of your other bicycles? When you let go does it snap right back or move slowly? Is it possible that you are just not used to a long cage derailleur?

some RD'd have alternative spring anchor holes, to preload the return spring more ..
the pivot at the bottom come apart?

Tighten the B screw?

Run those areas in the next bigger chainring, as long as it does not routinely cause acute cross chaining.

the the new shimano ones with the ratchet in them. "shadow plus"

when you pull the cage forward [towards the crankset] how does the tension feel compared to one of your other bicycles? When you let go does it snap right back or move slowly? Is it possible that you are just not used to a long cage derailleur?

It's nice and snappy. It's definitely working properly. But it does feel easier to move than on my other bike (old Shimano 600 short cage.) I've had mountain bikes before, but I've never noticed the amount of chain slap I'm getting with this setup.

I thought about tightening the b-tension screw. But won't that make my shifting less precise?

some RD'd have alternative spring anchor holes, to preload the return spring more ..
the pivot at the bottom come apart?

Not that I know of. It might, I'll check it out the next time I pull the derailer off the bike.

Are you sure you have the right chain length? I think shimano says over the front large ring and over the rear large ring plus 2 for MTB or something like that I forget (think ZINN says plus 4 for road bike?). This is a general rule to let you have plenty of chain, Im sure you could make it shorter but would make the chain under higher tension on the return (bottom) which might be what you want, but the RD will be taking more stress though.

Is it the chain slapping the top of the chainstay? Then the derailleur tension may be OK but the freehub/freewheel is binding. Have you rebuilt the freehub/freewheel lately? A spring won't just lose tension unless it's heated or twisted past its yield point, which is nearly impossible to do on a derailleur. A dirty freehub is more likely.