I finally solved the low power problem with the car that I experienced after rebuilding the head. It was found by accident. I finally had some time and decided to take the valve cover and check the cam and crank alignment marks. After turning the engine manually about 20 times. I noticed the marks align in some revolutions and not in others. I said what the hell, I'll just take the front timing cover and re-align everything again. I adjusted the crank to TDC and the cam aligned this time. I took the tensioner out and guess what I found? The chain was loose by one tooth on the side that has the straight guide. I knew immediately that's the problem. I pulled up on the chain and took all the slack on the right and moved it to the left. My timming chain is new and all timming guides and tensioner. No I know why the tensioner plug took a lot of force to screw in during the head assembly. It wasn't as bad this time. I put everything back, started the car and voila! It started and idled alot smoother. Took the car for a test drive and it had lots of power. It drove like a 2.6L should drive. Oh by the way, it shifts much smoother after the vacuum went up to a steady 16 in.Hg.
Thanks to everybody who helped me with this problem.