Porpoising is a front to rear balance issue. I'd take it to a scale and see where you are compared to the tire pressures, first.
With a 97, I'd replace all of the bushings for suspension/bed with urethane. You don't mention the tire pressure, but that along with shocks can make a big difference. I had Rancho 9000s on my previous SRW, but I think the Bilstein 4600s on my current truck are better riding.
I don't know who makes a sway bar for your truck, but others have noted that it makes a big difference. My F450 already has a very heavy suspension, so I didn't replace the sway bar on my truck, and it didn't seem my previous truck a SRW needed it either. They were both Fords, however.
Finally, check the tightness of the tiedowns since that can make a difference. Don't overtighten, but make sure they are tight enough.
