Put some baking soda in the water when you simmer your tripe. Not too much though. I added about 1tb to 2.5 quarts water and 1.75lbs tripe and the tripe practically dissolved after an hour of simmering.
Usuually it takes 2.5 hours for tripe to get tender. Next time I use half as much baking soda and keep an eye on how long before I check it.