Hi Colby, as far as gas mileage goes, please remember your engine is just an air pump. It spins around and doing so it sucks air in and forces it out. Air mixed with fuel that explodes at the top of each compression stroke. The more times you spin your engine around to travel a specific distance, theoretically the less your gas mileage will be because you're passing more air/fuel through it. There are some qualifiers to that statement, but if gas mileage is your goal low rpms with high torque is a good starting point. With that cam, you're going in the opposite direction (as Jerry...HotRod Lincoln and others) already said. That camshaft is going to push torque up into the high rpm band.
Take a look at your 5th gear---.74. Now take a look at your 6th gear---.50. Craig told you he runs around 2400 rpm at 65, and he is right about that...but Craig has no overdrive gear so he's running 1 to 1 in fourth. And so will you. It is when you go to 5th and 6th (if you can even use 6th gear) that things change. If you had Craig's 3.08 rear end at 2400 rpm in 5th gear, you'd be going about 88 mph and at 2400 in 6th, you'd be going about 130 mph. So obviously that rear end is worthless to you.
Now with a 4.56 rear end, at 2400 rpm in 5th gear you'll be going 60 mph and at 2400 rpm in 6th gear, you'll be going 88 mph. (assuming you have 28 inch tires, which is the lower of the two tire sizes you mentioned)
So if you assume 2400 rpm is going to be the happy spot for that camshaft, a 4.56 rear end will sort of work for you, but I honestly doubt you'll be doing much with 6th gear. You'll have to drop down to about 1900 rpm in 6th to be going 70 mph and that cam and your engine are not going to like that. Not even a little bit. What you're going to learn is that in 5th, your engine is running too fast for you to drive at 70 and in 6th it is running too slow. I made this same mistake once and it was a big mess. Ate gas like crazy and was genuinely irritating to drive on the highway.
Just think it all through. That cam is for a race engine, and if that's what you want go for it. If you want a 350 that will work with those transmission ratios you have, then get more of a stock cam (one that will pull your torque down to a lower rpm range) and at least a 4.56 rear end...4.11 if you must, but with a 4.11 in 6th gear at 2000 rpm (a nice target for good gas mileage), you'll be zipping along at 81 mph.
Now I've owned an S10 and while it was nice, it was not engineered to drive at speeds over 90 mph for any length of time unless you had a road as flat as a pool table with no wind. And that wasn't with an AD body sitting on it.
