HebaruSan

This looks fairly decent (credit to Krizzen on Reddit):

In general, going from Orbit A to Orbit B has the same cost as going from Orbit B to Orbit A, just in the opposite direction. This is because the magnitude of the burn is just the difference in your speed at that point in Orbit A versus Orbit B.
In the case of a return, you're essentially undoing the capture burn, which the map says is around 310 m/s, and which is not too far off from the 265 m/s from my screenshot. The tricky part is the timing; you need to burn at just the right part of your Mun orbit to do it that efficiently. If you then wanted to circularize at LKO after that with no aerobraking, it would cost the same as the initial burn to get an intercept, again because the two pairs of orbits are the same.

Your log file says you have two copies of MechJeb installed, one in GameData\MechJeb2, and the other in GameData\Squad\MechJeb2:
Try removing those.

You can only attach it to one, and it's always been that way. If you need it to be more sturdy, a strut at one end will hold it in place nicely.

The rear landing gear is too far back. It should be just behind the center of mass, so it's easier to tilt the plane up on it like a seesaw.
The craft has almost no pitch control. Try putting a horizontally-oriented control surface near the front or the back of the plane, or tilt those tailplanes more towards 45°.
Try using just one forward landing gear instead of two. With a 2x2 setup like this, KSP planes tend to lose stability as one of the wheels slightly lifts off the ground and the other then imparts a yaw force.

On the contrary, some of us enjoy building lifters and see questions like yours as opportunities to have fun. Thanks!
I copied your payload the best I could (leaving the tanks full) and ended up with this; spoilered in case you prefer to try it on your own instead...
 

If you're putting the gear on the wings, it might be an artifact of the wing joint flexing under the weight of the fuselage. Each wing effectively forms a lever with the wheel as the fulcrum and the rest of the plane pushing down on one side, so the further apart those things are, the more the joint will bend under that stress, which can bring the wheels out of alignment just enough to cause problems.
Does it get better if you add struts between the body and the wings? You wouldn't want to fly that way because of drag, but it would test whether this is the issue.

Map screen, click the 'i' icon on the right side of the screen to bring up info about the craft. Press 'c' or click the IVA icon on your pilot to go to IVA mode, there's a radar altimeter in there somewhere. Not available for unmanned craft. Press 'c' to go back to regular mode. You should be able to drag the icons around in the staging list, but I think that only works for engines that haven't been activated yet. However, press 'x' and 'z' to set throttle to 0% and 100% respectively without fiddling with staging.