That’s pretty heavy for 42000ft, but you could reach 36,000ft-38,000ft if you decrease your climb rate. Climbing at 2,500fpm is too excessive for that height which explained why your plane stalled. I usually keep it like this.
0-10,000ft MSL = 2,500fpm
(10,000ft-20,000ft) MSL = 2,000fpm
(20,000ft-30,000ft) MSL = 1,500fpm
(30,000ft-40,000ft) MSL = 1,000fpm
(40,000ft and above) MSL = 500fpm
Another way is to stepclimb, like multiple users have said. But if you want to get to 38,000ft ASAP with that weight you can decrease your climb rate every 10,000ft
Usually for a weight near to MLW, I wouldn’t dare to climb higher than 38,000ft. 38,000ft is like the highest altitude you can reach with such weight. For above MLW I would say it range between 32,000ft-36,000ft depends on your weight. If your load is less than 35% then you can climb to 42,000ft straight away (But remember to reduce your climb rate, otherwise there’s a chance you may stall aswell)