What is the probability of producing a tall pea plant from a genetic cross between two hybrid tall pea plants?

Tt xTt gives 3 Tall (Tt, Tt, TT) :1 short (tt) = 3 in 4.

since they are hybrid pea plants, they will not be able to produce a fertile, viable offspring

when you have a hybrid, there is a choice of three occurences

Reduced Hybrd Viability: offspring dies before "birth" or after ; it simply cannot survive

Reduced Hybrid Fertility: offspring cannot prouce; it is fertile

Hybrid Breakdown: the hybrid survives and is able to reproduce, but cannot produce viable offspring

idk if this answers your question or not, but its useful to know.
in other words, the hybrid generation will have to eventually cease; it can not evolve into another species