My two main concerns are the higher gas usage (higher revs = more crusing horsepower = more gas expended) and the higher cruising revs (more revs = faster engine wear.)

Most cars with quick final drives usually have a deep 5th to counteract it on the highway. I'd love to drop an 88-89 GTUs 4.3 into my car, however I would ideally need the trans from that car for it's special 5th gear and speedo gear.

Don't forget, with a different final drive gear, your speedometer will be off. My friend's BMW 2002 has new numbers taped to his speedo for this reason. :chuckles: