New Tranny or New Rearend?

[Tmwoodall]

I checked my gear ratio this weekend (its a roller, never been on the road since I owned it). It turns out I have a 4.10 rearend mated to a TH350 and a 350 SB.

From my research that thing is going to suck, and suck up the gas at anything other than city driving. My question is, should I pull my freshly rebuilt TH350, and find a 700R4 so that I have overdrive, or should I put in 3.73 (I have a used 3.73 ring an pinion in a box)/3.55 gears.

I know both will get me closer to highway cruising speeds, but I am not sure I am aware all of the pros and cons of the two alternatives. Keep in mind my engine should be hovering around 400HP and close to that in Ft/TQ.

I believe I already have a 700r4 drive shaft as the one that came with the truck was too short for my 350, and we had to move the cross member forward to install the 350, so that part of the cost equation has been handled.