KEEP AT IT. Don't sell your truck. Somdays I too get frustrated especially when i first put my engine in. it took forever to finally get it running and forever to work out all the bugs. I even had to change the oil pump and rear main seal shortly after I installed it. my front seal still leaks a bit, and at first startup i get a little puff of smoke because one of my valve stem seals is flopped up. I still don't get that great of gas millage either. BUT i think back to when i didn't have my truck and it makes me glad that i have it. I find that the more I touch and tinker with my truck the more depressed i become because for some reason I think its not as good as it used to be. but in reality, when i bought it the engine knocked, had no power, leaked real bad, and it was automatic. That rust on my floor was there before, there was just carpet hiding it.
So my advice to you is to think back to when you first got your truck and how happy you were. there may have been many flaws with it but it didn't matter to you at the time, you had a sweet Toyota pickup... guess what you still do, and now its got marlin bumpers and a fresh 22re amongst other things. AND you've got the sweet factory stripes (jealous). A New engine always has bugs to work out, I know i wanted to give up many times, but you just have to keep plugging away at it. Soon enough your going to hop in your truck and for no reason at all your going to get a big grin on your face and maybe not even know why. I get it when i punch it in second or third and it moves a little faster then I'm used to, or I deny some idiot from cutting in front of me by using my skinny pedal. Some times i just hop in and grin for no reason, just that it is my truck and i put all the work into it myself. you will feel the same as when you first got your truck.
You feel like you've wasted SO much money but in reality you haven't, that engine is going to last you A LONGG time and those bumpers are going to keep that clean body, clean. just imagine a huge dent/crumpled corner on the rear quarter or your bed. I know it makes me sick. Any hobby costs money, and yes usually you feel like you've wasted it. I've got a 1200 mountain bike i don't ride much any more and an RC car I've dumped too much money into and i don't even drive it any more.
My Truck is by far my most favorite thing in the world even though somdays I think it is the worst thing in the world. I'm sure you feel the same way, You just have to work out the bugs in your new engine and get it working well and you'll be happy. and yes you'll probably decide you want to get something else or something else may happen to it and you wont be satisfied until you get it out of the way. its just human nature we are never happy, or at least for long. we have to keep striving for something more.
So fix that motor and drive that truck you lucky SOB.
p.s. sorry for the essay lol
Shawn