Sorry to say this - but no surprise at all ....
In fact - I'm surprised you actually got of the ground.
I do not mean to be rude - but it appears that all the comments I and others have given has been put aside ....
You and Wildthing have given me good comments. I considered and evaluated all comments. Reading through all responses I considered each one as folllows:
1. Suggested Lower KV will allow a larger prop. Answer_The largest prop I can use is 6 inches. 7 inch props will hit each other.
2. Conduct a ground test to check temperature. Answer_I did this with the Brotherhobby motors before flight on 4S.
3. Motor too small and check prop angle for hitting deck. Answer_5 and 6 inch prop will hit the deck on this jet regardless. that is why I take off at the lowest pitch (upward) possible to prevent this. Once clearing the deck/ground I go vertical.
4. Look for a better motor in a slightly larger size. Answer_purchased two Brotherhobby 2806.5_1300KV motors.
5. Suggested Racerstar 2507 series motor. Answer_Performance data (Banggood) for 5X4X3 prop showed 1400 grams (49.5 ounces) of thrust. My minimum thrust is 1700 grams (60 ounces per motor) which was built into my specs for good performance.
6. Suggested building jets light. Answer_Had to constant reinforce weak areas of this plane which added weight. The jet is not over weight, MotionRc.com
have a F-35 Lighting II, 6S, 32' WS, and flying weight 2600 grams (92 ounces); F-15, 38"WS, flying weight 3080 grams or 108.6 ounces. I normally build my large jets (fully loaded) within manufactured model specifications.
7. Loved this last suggection_That larger/heavier models do not follow the same high KV as smaller/lighter versions. Answer_purchased two Brotherhobby 2806.5_1700KV (6X4X3 props) motors and I believe this will be my choice motor for this model. Light weight and plenty of thrust. This jet can accommodate the 6S batteries and still be within manufactured model specs.
I hope that I am not being rude, I loved every response.