350 Shifting to soon?

[Mertz]

?

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72 Chevy 3/4 ton pickup. I installed a quadrajet and it is working great. I adjusted the transmission cable with the throttle wide open and then connected the cable. I pulled a trailer for the first time today and going up a steep grade at 55 is down shifted up shifted and down shifted several times very quickly. When I got down to 50 it down shifted and stayed there until I got to the top of the hill. It seems to be shifting early without the trailer as well. I have a stock converter and rebuilt trans with a shift kit. Is the cable to tight?