Not much more
If the only things done to your trans are the addition of a Torque converter and an aftermarket valve body, then I don't believe your trans can safely and consistantly hold much more power. If the trans was completly gone through with lots of internal upgrades then add HP .
This is because the basic Dodge auto trans can be either a very tight, minimum clearance trans or a very loose leaky trans. It is a gamble and the luck of the draw when you buy your truck. Some hold up very well for over 100K, others die before 30K.
If you are williing to gamble then go for it, and be prepared for trans problems, maybe you will be lucky and not have any. Maybe not. I would suspect that you will have third gear problems or rear clutch problems.
How many miles are on the trans and truck??
Hope this helps, Greg L