Well when they first fought, Gaara wasn't in his right mind and was being influenced by Shukaku who he thought was his mother. After getting beat by Naruto and reflecting on things, Gaara began to be more in control and was fighting much more strategic. Sasuke was weaker than Gaara in the chunin exams, they fought in the ring and out and Gaara over all came out on top even if Sasuke hit him with Chidori more than once; that was Gaara not in his right mind as well.
Gaara is much stronger than before, just like Sasuke but if Gaara was stronger from the get go and only gotten stronger then Sasuke getting stronger wouldn't put him on top when only his stats increased. Gaara's stats increased, he became more in control which made him more strategic, Gaara shown new jutsus.
Sasuke's sharingan and speed would allow him to dodge Gaara's sand effectively but I don't see him dodging Sand tsunami, escaping the sand Gaara makes underground and could grab Sasuke while his attention is on Gaara, Hit Gaara who can hover in the sky, survive Sand coffin, or pierce Gaara's Shukaku shield. That's base Gaara as well, had Gaara used Shukaku mode, I think he would lose some control and go wild as he did against Sasuke before, he would have the power over all but might be lacking in the strategies but he can use air cannon, control sand, have increased speed, power, and durability.
