82 s10 305 swap

[mexlokote]

i have a 1982 c10 it had an inline 6 250 engine, i bought a 305,,
to be able to fit the starter i had to buy a new flywheel,

my truck originally has a automatic transmission,
before the swap i was driving the truck,,,
trans worked great and had no issues,

after i installed the 305 i try to set into Drive and it will move slow i mean slowwwwww sometimes it doesnt move but when i put it in reverse it does work great and strong, what can it be????