Always something new

So I recently got a new motor in m y truck and got it running right but then the transfer case was leaking and so I dropped it out and repaired it. I drove it around and no leaks or anything so later that day on longer drive the tansmission stopped shifting into high gear. Once it hits 30 mph the revs shoot up and it feels like the truck is in neutral. The motor is turning but theres no power going to the wheels. Then after I finally got the truck home there was oil all over the transmission. I couldnt tell where exactly it was coming from but it looked as if it was coming from in between the motor and transmission. Also I could not get the truck above 50 mph because there is no power getting to the wheels. The motor will be doing about 3.5-4 thousand rpm's and there is no increase in speed. My question is what would cause the oil leak and why would the transmission not be shifting or getting the power to the wheels?

Is it engine oil or tranny fluid that is leaking?

It sounds like a torque converter not locking up.

It sounds to me like your problem is the leak. If the transmission gets low on fluid it will quit going because, it has to have enough fluid to create presure. I would not drive it until you fix the leak and get the transmission full again or you will burn it up. I would start by checking the cooler lines for leaks, if not and it is coming from the front of the trans then it is probably the front pump seal. You will have to drop the trans to get to that seal.