Change order of your rules:
RewriteEngine On
RewriteBase /
RewriteCond $1 !\.(gif|jpe?g|png)$ [NC]
RewriteCond %{HTTP_HOST} ^www.gsmastersinc.com$ [NC]
RewriteRule ^(.*)$ http://gsmastersinc.com/$1 [R=301,L]
# Removes index.php from ExpressionEngine URLs
RewriteCond %{THE_REQUEST} ^GET.*index\.php [NC]
RewriteCond %{REQUEST_URI} !/system/.* [NC]
RewriteRule (.*?)index\.php/*(.*) /$1$2 [R=301,NE,L]
# Directs all EE web requests through the site index file
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /index.php?/$1 [L]
In general keep your 301 rules before internal rewrite rules.