I'm having a similar problem....This only shows on both the 752 and 753 of the CS757.
It’s been quite a while since I’ve used the CS version because of the poor sound quality (in my opinion) and the fact that the airline I worked for had no 75’s but several 73’s - therefore real life pilot help was freely available.

This problem does not show on the JustFlight757, QW757, or another company 73x series aircraft.

Based on a route using Standard airfields (as against hot and high) over a distance of 288nms, Flight time 45 minutes, FL270 limited by City pair - weights come out at around Payload 15000kg / ZFW 83000kg / FOB 7700kg / TOW 90600kg to enter into ACE.

After loading V2 becomes 139kt - CG 30% and trim 3.31 (+ or -) and the CI used is 30 (across all my aircraft)

2 things happen on take-off – The Roll is VERY slow, as is the Rate of Climb – in fact when I last flew the route the aircraft had only reached approximately FL100 about 20 miles from TOC - even though Cruise Alt was set on the ground. I try and engage VNAV and LNAV as soon after passing 1000ft as I can !

Any help appreciated