I did the same thing on both my 03 and 02 with respect to changing the standard oil out right away after purchase. My 03 had 30k on in when I purchased from dealer in 05 and never considered running standard oil again. I had to change out the valve cover gaskets around 130 K Miles "O those serve for clearance also for those thinking $100.00 is to "" much for V.C gaskets" Learned that the hard way.. anyways the inside was clean no build up. Regrettably I did not use quality gaskets and had to change them out again around 160 K miles, once again the inside of the cover was clean with no build up common with standard oil I.M.O.
Now I have an 02 which had 95 K miles on it and once again the standard oil was changed out to 5w 30 Full Synthetic. I will run any of the brands of F.S as long as they meet the API standards listed on the back and all of them do even the Walmart brand U.S but I prefer Mobile 1 or Pennzoil.
The high mileage comment above is correct with regards to oil leaks becoming an serious issue but I think you are well within safe mileage to switch over with out issue.
I am up here in Ontario now "no not do to D.T" and run 5w 30 but when I lived in down south I ran 10w 30 F.S once my 03 clicked over 130 K.
Back in the day I had a real C.J with high mileage over 150 K and there was noticeable engine wear noise. I decided to change over to the new Castro oil F.S..Wow you could here the db drop with respect to engine noise but that old jeep started to leak oil almost every where... had to switch back to standard oil.
Back to my recent 02 purchase and change to F.S - I can not find any M.M.O up here great stuff to clean out the inside so I resorted to a little transmission fluid with light usage before changing out the standard oil. Actually I did this twice no and feel pretty good the inside is clean. Some owners just drive there vehicle in to the dirt then get a different ride, not sure how that works out $ wise but you sure know when you buy one that was not Loved!!
