In 91, the 351 Windsor engine barely had enough power to pull it's own weight when new. Damn good engine though, and well worth rebuilding and some upgrades to keep things moving. At that many miles, I'd recommend a rebuild, with a good truck cam, and a good set of aftermarket cyl heads. If the budget is too tight for that, a rebuild with a decent set of pistons to bump the compression half a point might get You the power You need.
Good luck with it. Mac.