Here are some helpful links when it comes to modding your TBI
TBI Chips (http://tbichips.com/?page_id=73)
Tbi mods (By PMA4x4) lots of pictures (https://ck5.com/forums/threads/1991-5-7l-bored-tbi-upgrade-write-up-warning-lots-of-pics.301416/)
If you just want to rebuild your TBI (http://forum.73-87chevytrucks.com/smforum/index.php?topic=24770.0) Captkaos also has a good write up on that.
this is the spring Chris used in his write up (http://www.top-downsolutions.com/powertrain-performance/spring-for-gm-17113186-vafpr-(vac-adj-fuel-press-regulator))