timing ??

hi , newbie hear so pls bear with me . i have a 90 k1500 z71 with a

5.7L and th-700-r4 auto trans with 297xxxkm . i just bought the truck and it has a glitch . its a rebuilt trans 6 months ago by previous owner . new plug wires , cap , rotor , and plugs put in last week by me . here is the problem ... i start the truck and drive casually it runs fine , maybe a little underpowered . when i hit the gas to say , climb a hill or try to pass someone , the engine clacks like the timing is out before it will kick down a gear and the service engine soon light comes on . when i pull up to a stop sign it idles a little rough . i turn off the engine and start it up right away and it is fine again , and the ses light is off .. i read the codes and get #43 and #44 . esc is not getting signal from knock sensor and lean mixture . it suggests to change the knock sensor , but if that were the case , shouldn't the ses light be on all the time ? does this sound more like the esc mod , or am i out to lunch on this ? any help would be greatly appreciated . thx ,rukz