When I upgraded from 0.80 to 1.20 mtr dish I had to change the lens, difference in RX was huge, couple of dBs, DATV beacon was 4 dB different just because of getting the right lens.
Of course that lens is for RX, not your TX issue.
As trick from PE1RXJ to test the quality of the dish is simple, but with amazing results; when he compared 5 dishes or so: aim the dish at the sun, so need a sunny day, spray the dish with water, hold a piece of white paper at the point of the lnb. Some dishes create a nice bright spot on the paper, means focus, other illuminate the entire paper, not much focus/gain.
And so there are many many variables.
Keep going, its all about experimenting, and learning!