Rotella would be a prime choice, it has more zinc/phosphorus than the Mobil 1, and more additives, but a lower grade of base stock. The Rotella T5 10w30 is readily available at most Walmarts, the conventional Rotella 10w30 can be had on sale every few months at Advance AP for even less (right now I think). There is no difference between the two except the base stocks, add packs are identical and both will serve you very well. The T5 being a synblend has better cold flow, the fact that it's available anytime you want at Wally's for a good price is a bonus too.
The Mobil 1 High mileage mentioned previously is probably the best synthetic match for the 4.0, I'm not a fan of Mobil in the 4.0 but the HM version does well according to others. You'd be better off with the 5w30 and a booster quart of 10w40 though, you'll get better base stock, higher VI (cold flow) and still get 10w30 thickness and performance in the heat doing so. Valvoline Maxlife full synthetic supposedly exists and would be a great choice also but good luck finding it at a reasonable price.
Everybody has their opinions on oil, that's what makes discussion fun, and I disagree with the idea Castrol HM is not a good choice for the 4.0. I don't believe the zinc number posted is accurate, but it will certainly have less than Rotella or Mobil HM, it is however very thick for grade with a high viscosity range. Your own experience with it as well as mine has been positive, and I've seen a number of used oil analysis on it in the 4.0 that indicate the 4.0 does very well on it. Valvoline Maxlife (the common red bottle syn blend) is somewhat similar but thinner, it also does very well in the 4.0.
Pretty hard to make a "bad" oil choice these days. My 4.0 actually runs quietest on plain old Pennzoil, several other Jeepers have experienced the same thing, lots of good options out there and you don't have to spend 5+ bucks a quart for many of them.