you must have a 2 wheel drive.
You can keep your 14 inch wheels and get large enough tires to do anything you want. Plus tires for the 14 inch size are cheaper, generally speaking.
I know, for instance, that BFG makes a mud and a/t tire in 28x9.5 r 14. This would be a good increase over your current size and give you a bit more clearance as well. Should have no affect on power/computer/transmission characteristics, etc.
By the way,
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