Many transmissions have fluids that are cooled using the same process that your engine fluids use - the radiator system. Transmission Fluid is special in many ways. When you first start your car, the fluid is not yet warm. Many transmission systems share the cooling system with your car, so if it is running hot, your transmission fluid will suffer. It could also simply be that your transmission is low in fluids. In any case, your fluids are probably the source of the problem. Whether low or just getting hot for one reason or another. They need to be replaced and the transmission fluid and cooling systems need to be checked. This usually means that the fluids, filters, seals and possibly other components inside the transmission need to be replaced.
Means that the transmission is delaying going into the next gear.
Transmission temp sensor can cause a slip or high rpm before shifting to next gear.
because the transmission is going out, it need rebuilt or replaced
Yes. From low fluid, plugged filter, or an internal failure.
I'll assume you mean an automatic. If so, there are friction plates inside the transmission that get worn out and just like old sand paper gets smooth and doesn't do it's job very well, the friction plates get smooth and don't grip anymore, causing the transmission to slip. In the possible case it is a standard transmission, it isn't the transmission, it's the clutch slipping.
I had my transmission flushed and now my 97 Voyager will go into reverse and doesn't slip anymore. Was doing that until it was warmed up.
A 1994 Mazda Miata's automatic transmission may slip in 4th gear if the bands are heavily worn. When the bands become worn, they are unable to grip properly and cause slippage.
My cam synchronizer failed and it was causing the trans to shift erratically and to slip
The bands may be weak, it may be low on fluid.
If the gears are slipping on a 1995 Honda Civic then the transmission is worn. The transmission will either soon need to be replaced or repaired.
If it is causing the trans to slip, it could.
This more than likely your transmission starting to slip. You should take it to a reliable mechanic to fix this.