...do I need? (title got cut-off....)

I have a 1990 G20 5.8l 350 V8 Van -

Napa gave me a 195 degree thermostat / I called them before installing because it didn't look exactly like the one that came out and I couldn't verify online that it was the right one.
They confirmed that's what they have for my van.

Never the less the van runs pretty cold, taking a long time to get to half it's normal operating temp, heater blows sort of warm even after 5-10 mins; it's running boggy and less powerful then I am used to. Also it's a bit fumey smelling. It basically has all the symptoms of a bad thermostat.

I have a few hundred miles to drive soon and I wanna get it swapped out but having trouble pin pointing the best one to install.

Since there are apparently many options here's some of what the van will be going through if it matters - pulls a small trailer for 1000's of miles at a time, often through mountains, spends most the year texas. usually goes 4-10k miles around the country every year.

 

Unless you are running up an down hwy 83 shouldn't have any long pulls. On a tbi engine almost anything can make it bog. Vacuum is biggest culprit.
You should make sure your throttle cable has no play thru wot and learn to adjust TV cable too.
Use a flashlight to make sure both injectors have a cone shaped spray. Don't know if you have a knock detector detector but it can retard your timing. Even thought I use a Accel coil mine bogs when plug gap is over .040 and I have zapped a couple of ignition modules.
Find-troubleshooting the tbi engine, in PDF online to download.
And of course make sure your pink wire has 12 volts

 

Sold the van in 2019 and just bought her back again this week! very rough shape so I'm back to scouring and posting on these forums.
and this is all great advice in general; thank you.
I wish I could remember what I did to remedy this problem in the end...
Will dig through notes and post reply for future generations if I can find it.