Considering re-gearing my c20

[bry593]

Originally Posted by HO455

I was told by Extreme Automatics that 2004r's are great transmissions but will not tolerate towing.

Correct. GM never installed a 200-4R in a truck, let alone a 6700 gvwr for good reason. Remember, the 200 is based on a TH200, the 700-R4 on a TH350, the 4L80 on a TH400.

The 700-R4 is mostly same as 4L60, although 4L60 has stiffer apply plates and more friction discs. This was the reason the 700 got a bad rep. Towing would cause 3/4 disc stack to slip and burn. The 4L65 is same as 4L60, but with 5 pinion planetaries and improved sun shell with thrust bearing.

So, might as well put in a 700 with 4L60 disc stack and slightly higher apply/system pressure. With a cooler, this would be equivalent to your TH350.

If you want tow without fear in overdrive, 4L80 is preferred.