I've never seen a oil cooler for the 3.8's but that's not saying you couldn't make on for it. But if your just making short quick climbs on hills and it returns back down quick I think your OK.
Mishimoto makes one, but it's a bit pricey. I think I'll put some Lucas stabilizer and leave it for now, like Largehit does. I'm with you... as long as it returns down it's pretty normal. I'll just watch it. Depending on where we camp, there's a canyon here that's a few miles long.