Wow...

I almost looks like you have a bad spring, or a crack in one.

But, I would probably pay a good, independent shop and get an opinion.

 

both springs are in good condition, none of them are broken or cracked.

 

I've watched some of your videos and the van is turning out really nice. I will caution you that the materials you are using are much heavier than a conversion has so you should get the van weighed to see where you are at. The only other thing I would suggest to do is add a power ceiling vent before it is too late. That is the #1 thing I use in my van when camping.
Steve

 

Something is definitely wrong is your springs are good......

here is what my B2500 looks like

pretty even, and I think my rear springs sag

 

i don't have enough yet to buy the fantastic fan and max air vent, i do already have the wiring in place for one.
i don't have seats, tables or heavy counter tops, i also don't have a heavy larger fridge, convection oven, regular oven, large black tank and large propane tank.
the wood is 1/2 inch and 1/2 inch with very little 3/4 inch, i have a low top not a extra weight high top so it should balance out.
i won't be in the van using it until it is fully complete, right now it is just my daily driver.
the suspension handles normal, no issues with the back being weak.
it was the same height when i got the van with nothing in it.
i am going to check with a company near me that makes leaf springs, they can make heavier duty with extra leafs and taller shackles that can clear the filler neck.

 

that is a shortie 3/4 ton, the suspension is not the same as mine.

 

Rockauto has husky helper springs for $77 plus shipping for the set with hardware, it says it increases weight capacity by 1000 pounds and no height change with a load.

since my springs are not broken will these helpers bring up the height?

 

Perhaps you could post photos of your rear axles, u-bolts, shackles, and springs. They may have been re-installed incorrectly. My van is longer and heavier than Jimbo's and it sits at the same height.
Steve

 

I just had a smog done on my van, and the paperwork said it was 4250#

 

ground is frozen and it is freezing out so i can't get under it today.
i checked the springs when i had a couples used tires put on.
they are on the top of the rear end and everything is there, the Ubolts are tight, the plate is centered on the pin and the shackles are done right with good bushings.
the springs are straight, not sagging and no curve to them at all just perfectly straight, they should have some curve to them.
they are not brand new but are newer than the van if that makes sense.
i am thinking about getting a custom set made, the shop near me makes springs and U bolts on site.
i just can't afford over $500 for springs which is why i hoped helpers would work,