Put a 4.0 in it? Sorry, had to do it. I have a 3.0 so I'm allowed to kid you.
Better filter, intake tube, chip, exhaust -- all the standard stuff. Cams of course, roller rockers -- there are lots of performance things you can do.
Most of them do just a litter but they all add up if you do several of them. Take a picture of your MAF and post it. I know the 4.0 MAF's are integrated, but I haven't seen a 3.0 MAF from that year (I don't think -- unless I'm forgetting).