I replaced the fuel pump and ecm. The codes that still come up are 54 and 55. It will not start. What do i need to do

What is your question?

The vehicle sat for 6 months. When I started driving it again it was harder and harder to get it running.

What makes this problem better or worse?

Always

How long has your 1995 GMC Yukon had this problem?

It sat for about 6 months. When I started driving it again it started to get harder and harder to get running.