Gaara has been battling non stop in the war and is still going and now facing 5 madaras..... his stamina is just as good as it was then
if you forget, him and naruto surpressed their bijuu chakra in part 1, the only time naruto used it, it was clearly visible it wasn't his chakra same with gaara, he transforms into the shukaku when using it.
Gaara has gotten stronger, his abiltiy to control masses amounts of sand was mistaken by the 4th kazekage(edo) to belonging to the shukaku, someone who had fought the shukaku countless times mistook gaaras for it... His sand has gotten faster in the fact that when deidera tried to destroy the whole village, in a split second gaara provided a whole lot of sand to protect the WHOLE village.
Gaara has gotten faster, stronger and more intelligent with his techniques and battle strategies, not to mention now gaara can fly with his sand leaving kimimaro stuck on the ground to be bombed with sand attacks.
all kimimaro is healthy, thats only more stamina