26 is probably too much prop for that rig, especially in the summer. They make a 4 blade prop that may be a good alternative. My advice to you is to test every prop you can get your hands on. No two props will run the same, even the ones that are marked the same on the box.
Also keep in mind that heat & humidity zaps 10-15% of the power from your motor. There is a noticeable difference in how your motor performs in July versus December.
If you don't want to buy another prop, talk to a good prop guy like Josh at Steve Propeller or Bobby at B & B Props in North Richland Hills. They can most likely take the prop you have and tweak it so it performs much better than stock for not much $$