I asked a similar question just a week ago. Looking over the article on transformational epic classes, this is a difficult class to make epic. I would suggest dropping the "certainty" aspect, if not your penalty can quickly outstrip your saves and attacks -6 is pretty steep as it is. I would continue the transformation to the tome of blood version of pseudo natural for the first two or three levels and then I would raise Dr by +1 every four levels, meta magic every four levels add an extra summoning maybe ever four levels .
Some thing like this
1Acid resistance 20
2True strike, alternate form
3DR +1
4 Meta magic secret
5Extra Summoning
6
7DR +1
8Meta magic secret
9Extra Summoning
10
11Dr +1
12Meta magic secret
13Extra Summoning
14
15Dr+1
I still havent been able to come up with anything for level 6, 10 and 14. What do you think. Altough I would love to see one in which the epic level pseudo natural template was used instead of the tome of blood, but that opens a ton of balance issues.
-KCM