Adjusting the trim tabs would help. But I would play around with battery placement. It is recomended that you break off the front part of the battery tray ( I comes right out with needle nose pliers, just jiggle it a bit) so that you can move the batteries forward. I have heard to use the lower motor mounting screw as a guide to place the front af the battery up to as much as 3 inches from the stock position.
I use the former as a guide and it has been a good starting oint. Props, weather conditions etc. will all come onto play. So you just have to see what works best for you.
I never got to use my stock prop as it broke when I first got to the pond. I have tried a few but the Octura x440 -3 blade prop is a good all around prop. There is a good prop thread on this site for the SV27., in fact there are a LOT of threads for the SV. Use the search function and have fun.
I haven't had a throttle issue, could be the drive train binding a bit, you can see how the flex cable enters the stuffing tube, is it straight?
could also be radio glitching, or batteries not fulliy charged? I am not the expert here jsut a couple of things to check out.