ok this may be a lil long but help please ... after installin my 4.10 a week ago i finaly got the nerve to open it up had to do a break in on it lol...so i pull out normal and go into second and then tromp on it ..wow it will pin you back in the seat. But.....rigth before i shift into 3 it seems to just fall on its face at about 4500 to 5200 .Apon heavy acceleration it will hold you their then after spinnin it goes good then just seems to let off.then engine is smooth no rough idle or ticking at all. maybe a tune up will fix it..Also my tranny is badd to my knowledge my sncros are bad and possible clutch.. could it be my clutch slipping ..cuz it seems to be reving normal but doesnt seem to have to ummmph it use to have any help we be appreciated

 

Sounds like a clutch to me.