I have a E350 with a 460 and it has a tendency to heat up on grades. It is stock with the stock trans, oil and power steering coolers. I'm think about adding another trans cooler. I can't decide to...
Granted mine is a class A, but I put it right at the grill and added a fan. I also bypassed the radiator portion of the transmission cooler so as not to have that added heat to cool. Mine is a 454 Chevy setup. I do not have a tranny temp gauge so I don.t know how much it helped, but the MH engine temp does not get as hot as it used to. I got my cooler from NAPA and was pleased with the ease of installation.