Take a look at the Theta Sk bib pants from Arc Teryx. I bought mine about 4 years ago in a medium tall size and they are still going strong. I am 6' 2", 185 lbs and a 33/34 waist. They are VERY expensive, but if you have the money, they are worth it.
I tried on both the large tall and the medium tall in that model. The large was a bit baggy for me, but you might need the large, not for the waist, but for the added length since you are 6'5". The also make non-bib but still suspendered versions. I would highly recommend that you try both the medium tall and large tall in any of the models that you might be interested in since there is some length and waist variation between the sizes.
Having said all this, you might have troubles finding the tall versions at retailers. You might be able to find an online store with a liberal return policy. Order both the large and medium talls from them and return the one that has a poorer fit.