Jim, If your engine is not as strong as before your head work then something is not as it should be... I know it is not fun to retackle a job like that... but you can take one item at a time... like the injection timing and recheck it.... this mystical " weakness in the lower end" is just that.... unless you have a bearing go out... or something like that... there is no way for the lower end to show up its " weakness ".....so buck up your courage and go back in there so you will enjoy your car again... not have that nagging feeling something is not right.. because in fact ... something is not....