Interest rates on truck payment...40%

I did the lender kept saying we'll get to that and the dealership kept saying that's between you and lender.

 

Well my payment is $1,800 a month.
The truck has new paint
New tires, king pins.
Needs an alignment as the steers wore out in 2 to 3 weeks and I've just put a new set on.
I'm pretty mechanical, I've pulled engines and trans bur on a truck everything is bigger and I don't have a suitable place to do my own work well at least a engine rebuild. I thought about building my own engine hoist/crane if I do.

 

At 40% interest I've calculated I'll be paying another 17k above purchase price.
I guess if I pay a ton or much more before each payment due date every month I could
effectively change that?
Can anyone point in the direction of someone that might rebuild the engine on down payment and credit?
I live in Ohio.
I did read the bad reviews about the dealership.
Maybe the interest rates not as bad as I think
I paid $2k
576.85 went to principal
1,423.15 went to interest.
I bought the truck at the week before Thanksgiving.

 

I don't know any of that, but it's said to have 475hp and to have passed their test for blowby standards.