If you are having heat issues I would definitely do something different! If the other cooler doesn't work, what about a hydraulic oil cooler? They will be more pricey, but with limited forced air-flow the "bigger-is-better" approach may be the way to go. A hydraulic oil cooler will also be tougher built. Maybe a spoiler between the frame and the rocker to force some air over the frame if that is the way your fan pulls. Are you using a trans temp gauge? Now I really wish I was going to the diesel drags!
Edit: Sorry, I forgot to add this
link. Have you seen the PPE truck?