I was wondering if anyone could tell me (other than shortening the drive shaft, adding a cooler, converting to a solid flywheel) if there will be any obstacles in converting my 97 ford f350 from a 5 to a 6 speed transmission? I like the idea of the real low 1st gear and the taller overdrive.

I've test driven pickups with the same engines and rear ends but one had a 5 and the other a 6spd. As far as I could tell 1st gear or "L" in the 6psd were the same ratio and so was OD. I think the gears are just closer together in the 6spd.

Yup, "low" (1st gear) and OD are almost the same for the 5 and 6 speed trannies. The 6 speeds just have slightly closer gears inbetween.

GM 5 speed nv4500 hd mw3
Gear Ratios:
<TABLE border=0><TBODY><TR><TD vAlign=top align=left rowSpan=7>http://powertrain.gm.com/images/clear.gif</TD><TD vAlign=top align=left></TD><TD vAlign=top align=left rowSpan=7>http://powertrain.gm.com/images/clear.gif</TD><TD vAlign=top align=left></TD></TR><TR><TD vAlign=top align=left>First:</TD><TD vAlign=top align=left>5.61</TD></TR><TR><TD vAlign=top align=left>Second:</TD><TD vAlign=top align=left>3.04</TD></TR><TR><TD vAlign=top align=left>Third:</TD><TD vAlign=top align=left>1.67</TD></TR><TR><TD vAlign=top align=left>Fourth:</TD><TD vAlign=top align=left>1.00</TD></TR><TR><TD vAlign=top align=left>Fifth:</TD><TD vAlign=top align=left>.75</TD></TR><TR><TD vAlign=top align=left>Reverse:</TD><TD vAlign=top align=left>5.61</TD></TR></TBODY></TABLE>




GM 6 speed ZF S6-650 ml6
Gear Ratios:

<TABLE border=0><TBODY><TR><TD vAlign=top align=left rowSpan=8>http://powertrain.gm.com/images/clear.gif</TD><TD vAlign=top align=left></TD><TD vAlign=top align=left rowSpan=8>http://powertrain.gm.com/images/clear.gif</TD><TD vAlign=top align=left></TD></TR><TR><TD vAlign=top align=left>First:</TD><TD vAlign=top align=left>5.79</TD></TR><TR><TD vAlign=top align=left>Second:</TD><TD vAlign=top align=left>3.31</TD></TR><TR><TD vAlign=top align=left>Third:</TD><TD vAlign=top align=left>2.10</TD></TR><TR><TD vAlign=top align=left>Fourth:</TD><TD vAlign=top align=left>1.31</TD></TR><TR><TD vAlign=top align=left>Fifth:</TD><TD vAlign=top align=left>1.00</TD></TR><TR><TD vAlign=top align=left>Sixth:</TD><TD vAlign=top align=left>0.76</TD></TR><TR><TD vAlign=top align=left>Reverse:</TD><TD vAlign=top align=left>5.23</TD></TR></TBODY></TABLE>