Thanks paedbo.
No I can't give any gas because the engine is at max rpm so if I give it more gas it will only stay at max rpm?? or maybe i'm wrong here, the strange about this problem is that the engine revs up to max with no gas. You are correct about the one way bearing on the second spur gear that it may slip. But the engine shouldn't rev to max because of slipping one way bearing and clutch.
When the engine are at max rpm I don't want it to engage the drive line, if it do that at that rpm I think I will blow my gearbox so when this happens I rush to truck to cut it of.

Thanks for your respond and I will test them next time it happens.