Moving from front to back, there is the engine cradle, then there is the cross-member the ends of the radius arms go into, then there is the transmission mount. The cross-member the radius arms bolt to has 4 bolts on each side.... I can't really think of any other cross-members that should be under your truck, and all those cross-members sit side to side..... do you have a picture?
Honestly, you must be talking about the one the radius arms bolt into, because that should be the only one that could interfere with your front drive shaft, and not be after the transmission, unless of course you are just talking about a skid plate that someone added.