4.5 lb isn't terrible for a 40 slab. I revitalized the famous Gator Skin Chakk last summer and it came out a couple of oz. heavier than that and everyone still had a blast with it at last years Ottumwa ProBro.
For Lipo batteries, some people think Thunder Power is overpriced for what you get, but I really like them and I buy all mine on the 50% off black Friday sale they have every year. The sale the price is comparable to all other brands pricing. All my batts in the last 5 year have been Thunder Power and they're light and perform great for me.
I used some Hobby King Zippy compact batts for a project a few years back also because they were the only ones that had that size in the MAH I wanted so I tried 6 of them and they are working great also, but I go easy on my batteries!!
To your wood or plastic propeller question on E props, I'm using plastic or composite for 13 inch or under. For E props larger than that, I highly recommend staying with the wood props, as the plastic ones get flexy and can cavitate. I like Xoar, Sail or even the Hobby King E wood ones are working good for me.
That's odd. You say tail heavy, but it pitches down. Usually if it is tail heavy, the plane will pitch up.
Usually with a profile, like your Mojo, you don't want any motor down thrust or right thrust. I'd take that out and make it as straight on as possible - that is how I set up all my birds.
It definitely sounds like your down thrust is causing that.