Here's my lifter for my Orion vehicle: On the pad. In orbit. I didn't make it to look like the SLS though, as it was meant to be part of a family of multi-purpose crew vehicles that I built. This one can get to Mun orbit and back with quite a lot of fuel to spare.
The resources tab. I've had this problem a few times before, and I'm using a stock game. It's particularly annoying when it happens while I'm using an ant engine (which is where this bug usually occurs for me).
I've done many slingshots before. Just use the maneuver nodes to help you. Minor changes to your orbit can get you to places without having to get the window right.
On Duna Upright, jettisoned the rocket cap and preparing for launch. Liftoff! The rocket then rendezvous with the orbiting return booster and flies back to Kerbin. Thanks, but no thanks. I have my own little company.