Q: wont go faster than 45 mph no power on 1990 Ford F-250

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
no power going up hills
(1) Answer
First thought is to check the exhaust to make sure it is not restricted.

Second thought - is the transmission not shifting properly?

Third thought - check for fuel pressure, basic tune up items.