Funny to find this topic. Just last night I was reading the 4L80E technicians guide and thought "hey, I could make this thing a six speed" so I came searching...

I haven't bothered to work it out fully, but by installing a 3/2 solenoid valve in the overdrive clutch hydraulic feed with the right controls it could be done - with the exact applies list a few posts up. I haven't even tested out my own trans controller yet, so a six speed conversion is way down the list.

I don't think they _had_ to change the gear ratios, I guess it was more a case of spreading the shifts more evenly - although they don't look too bad anyway.

The original ratios are:
1. 2.48
2. 1.48 (60%)
3. 1.00 (68%)
4. 0.75 (75%)

The new ones would be:
1 : 2.48
2 : 1.86 (75%)
3 : 1.48 (80%)
4 : 1.11 (75%)
5 : 1.00 (90%)
6 : 0.75 (75%)

James