When I changed my spark plugs at around 70K miles, I used the Autolite Double Platinums. I, as you, did found the original plugs with a huge gap. The truck was running fine but decided to check one plug to see how it was doing. That told me to change the plugs right away.
I accidentally gapped the new plugs tighter than spec. I think it was around 0.059. I was concerned after I figured out it was not to spec but I was too lazy to go back and re-gap them. The truck ran great with no issues and I don't recall any change in gas mileage. The mileage is near 120K now and the truck is still running great. The plugs are probably worn enough to be in spec now but I will be pulling one of the plugs soon to see what it looks like.
I changed the spark plug wires at around 100K miles. When I took it out for a test drive it suddenly started misfiring under hard acceleration. When I got it back home to check out things I found one of the spark plug wires was not seated all the way on the plug. Apparently I did not get it all the way seated and it vibrated loose. That solved the problem and all is well. You should consider changing the spark plug wires. They can cause misfire issues if they are not in good shape.
I think the 4.0 SOHC engine is a great engine and plan to use it for at least 300K miles. It has plenty of power for my needs, which includes towing my race car all over the country.
2002 FX4 Bright Red Supercab 4.0 SOHC, manual 5-spd & Tcase, 33" BFG MTs, K&N air filter, Modified air box inlet, Gibson SS cat. back exhaust, Bama flash, Hidden Hitch round receiver, Rear helper air springs, Electric trailer brake controller, Line-X bed liner, WAAG bar with KC lights and Wildernest shell.