ok i just got my magna back with a new gear box but now under full boot when u drop it back soemtimes the clutch slips some times it dose not is their any adjustment? or do the lines need bleeding? or do i need new clutch ? was not slipping when it went in for the new gear box

Yuor clutch is probably getting tired as all clutches do and if you were having gearbox problems before they woudl be affecting the power output of the vehicle possibly.

Also the action of removing and refitting possibly the clutch has disturbed it and its said enough possibly.