Recently replaced my really old 1965 Chevy Van (w/292-TH350) which I towed with since 1988 with a "newer" old '94 GMC Suburban. Van is still going strong but it doesn't have A/C. Much prefer the pre-OBD II vehicles so I can work on them myself. Burb has 126,000 miles, one owner, always garaged, looks new inside and out and mechanically in great shape. We have the Carfax that shows maintenance records from day one, old owner put new trans fluid, antifreeze and brake fluid before he sold it.
Engine sounded "good" but had no power. Found that the, plugs, wires, cap and rotor had never been replaced (the one thing the original owner didn't do). Tuned it up, added MSD adjustable timing control and installed a "fastchip" computer chip which made a huge difference. Lots of power now. "fastchip.com" out of Oklahoma customizes the chip for your vehicle. You have to send them your computer serial number so they can send you the right chip, plus they need to know your rear end ratio. I've never bought something for my vehicles that made such a major difference in power. Only was $159.
Love old trucks.