190e Transmission problems

Hi, I have a 92 190e. automatic. I bought it with 700$ from a lady, she did not put any water, and the engine blew. i bought another engine for 700$ with 100k miles on it. i had my cuzin install it. the car seems to work fine but when i put it in drive, i start driving.....and sometimes it does not change the gears...it does not go into second or third sometimes,i have to let go of gas and then it changes....any idea what i have to do? i was thinking the transmision overheated of something...? should i buy another transmision..i dont really want to do that....



thank you in advance...any sugestions will be very apreciated:)

and will it be hard to change the transmision? i was thinking of converting it to 5 sp? any ideas? will it be hard? what do i need in case i want to conv. to 5 speed?