I have first-hand experience in this matter. in June 1988 I was afforded a cab ride in Challenger 3985, from Dale Cut, to the Summit of Sherman Hill and through Hermosa Tunnel. We were accelerating as we had just gotten a green near the east portal. Inside was a light show of sparks flying into the cab. Former Railfan editor Jim Boyd and I met each other with laughter as we both were black-faced. Most of was diesel exhaust stuck to the tunnel roof that the exhaust had knocked down. As for 4014, I wouldn't worry cause they will likely have light throttle and some pushing help! The west portal is downgrade since the summit is in the tunnel.
Greg