2000 Holden Frontera Transmission problem

My car has an automatic gearbox and I had the gearbox re-conditioned approximately 30,000kms ago.

I recently have started to have problems with what appears to be the transmission although I am no expert. The problem occurs when.

1) I initially start the car, the gearbox is slow to go into gear
2) When driving the car, if I accelerate the car rev's as if in neutral before slipping into gear

Any information is greatly appreciated

jon