"also is" at the end of sentence

Your sentence is grammatical, but not very idiomatic, at least in US English. My impression is that in ordinary speech:

• too is used most frequently, almost always at the end of the clause:

Bob's driving, and John's driving too. or Bob's driving. John too.
Bob's driving, and he's buying the food, too.

• also is used less often and is usually put before the added element:

Bob's driving, and also John. or Bob's driving. Also John.
Bob's driving, and he's also buying the food.

In formal writing, you may put also just about anywhere, and you may put too immediately after the added element. You may put either at the head of the clause:

Bob's driving. John, too, is driving. or John is driving also. or John, also, is driving.
Bob's driving. Too, he's buying the food. or Also, he's buying the food.

All of these displacements are very formal, however, and should be used sparingly: perhaps only when needed to point the structure of long propositions.

Per my comment to the question, Google Books, and mine and TimLymington's "inner grammarians", all seem to agree that it's better to end the sentence with is also, rather than also is.

Personally, I think "I am glad that Gabriel is too." is much better, but I can't really explain why.