I have a 1999 ram 1500 5.2l with the 9.25 355 rear end I would love to swap it to a 390 but I'm not sure what to do with my dana 40 or 44 front not trying to tear up my 4x4 just wanting more ***** in this thing

 

You would have to change the gears in the front axle as well, or, never use 4x4....... Mismatched gears would break stuff in a hurry.

 

Do you have any idea what front axle matches a 390 rear

 

Gears don't care. If you have 3.90 in the back, you need 3.90 in the front as well. I can find 3.91, and 3.92.... Likely 3.92 in the rear, if its stock..... But, either way, you want MATCHED gear ratios.

 

And if you're going to change gears, why not go a little further and go with 4.10 gears? Works nicely with 33" tires.

 

cause something tells me 410 would probably slow me down on the interstate where as the the 390 gear would give me more torque than I have now but not lose my top speed is what I was told

 

Thanks now I just gotta find em seems like everyone ended up with 355s in 99

 

I guess it depends on what size tire you're running. With the OD auto tranny, you'd definitely not be losing any top speed on the highway with 4.10 gears and 33" tires.

 

With 4.10 gears and 33s your top speed will be way higher than you need to go, well over 120 mph.

 

Yeah; I was on the highway today doing 80 mph for a little bit. With 4.10 gears and 33" tires, I was a little over 2500 RPMs (below 2800 RPMs).

I actually sometimes wish I had 4.27 gears (not sure if they even make them for the 9.25), but I'm happy with the 4.10.