The 3715 was the earlier version. It didnt have as much options as the 3815.

 

I feel the same way. I expected MUCH more after installing the 3865, but can hardly even notice the difference!!! I am getting a little better gas mileage though, so I guess that will pay for itself in the long run
Im using the 91 tune also

 

I've tried the 87, 91, and 93 tune and didn't notice anything beneficial. I should mention that when I had the 93 tune on I noticed a lot more top end power. It really ripped when I brought her up past 4000rpm, but 99% of the time I'm not pulling that many rpms, so it really didn't benefit me at all.

I didn't notice ANYTHING when it came to low end improvement. It was a turd before the tuner, and it's still a turd now.

Putting my stock air filter in after running a 14x3 brought back my low end, but the tuner did nothing for me.

 

I have the 3715 and I could really feel the throttle response, and mid range power. I have to either get mine updated or trade it for a newer one through SC though.