Horse slowing down what would you do?

I have a 18yr old gelding that i barrel race when we first started out this summer in our shows we were doing great he got excellent times and we were at least winning enough money to cover our entry fees and fuel to get there but as the summer wears on he seems to be getting slower and slower,he isn't lame in any way shape or form and still is in excellent health and acts half his age he still acts all antsy to get in there and do his thing he fights me a bit and dances and prances he even sometimes gives a small rear and a leap forward and flies in there like he is really going to tear that arena up but he just slows down A LOT out there it is almost as if we are in slow motion going around the last two barrels and heading for the gate i see many people using over and unders or quirts out there to make their horses run faster and have a quirt of my own but i don't use it on him he is my buddy and i feel he is giving it his all i don't feel the need to beat him to win i figure if he is slowing down and not running out there like he used to then there is something he is trying to tell me maybe he is trying to say he is ready to retire but the wanting to get in there and do his thing so badly makes me feel otherwise yes i urge him with my voice hands and give him a few kicks but i WONT beat my horse so please don't even suggest using one on him .He is on a performance pelleted grain by nutrena that is for senior horses the stable he is kept at doesn't have very much gr in his turn out but he has free choice beautiful green freshly baled hay at all times and i supply him with electrolytes in his water in between cles,i don't know what else to give him or do to give him that pep in his step he had earlier this year in the beginning we were turning and burning now we are lucky if we stir up a little puff of smoke