This is the first vehicle I've modified for performance gains that has leaf springs. Earlier this year I swapped in another engine and has about 10k miles on the swap so far. A couple weeks ago I noticed a slight swaying from side to side during wide open runs, this has gotten worse to the point where wot runs feels like the truck will turn sideways. Made 349 rwhp on the dyno yesterday so I know its not the wheels spinning on wot highway runs.

Anyone ever have this problem? I'm thinking maybe the leaf spring bushings?

 

What vehicle? Bushings/hangers would most likely be the cause. Less likely but possible could be frame flex. I had about the same power in a 2000 RCSB, but AWD, and it launched and drove straight as an arrow. Maybe because I was only running about half the power to the rear axle.

 

2005 rcsb 2 wheel drive. Has rear eibach shackles.

 

Alignment good?
I know it sucks throwing parts trying to troubleshoot issues but I think you're right to start with the bushings.

 

Front end alignment is good.

 

Ever had a four wheel alignment? I'm wondering if the thrust angle is off.

 

I wasn't aware anyone does an alignment on a solid axle leaf spring truck....

 

The rear doesn't necessarily get alignment changes but having all four wheels measured makes sure they are all pointed in the same direction. During one alignment the shop found my rear axle to not be pointed perfectly straight and I had to replace a bent spring. It's a bit of a stretch but something to check.

 

i'd start by getting under there and looking for any loose/worn out parts. you can go well past the 350 mark on leaf springs. there have been 900+hp trucks on oem leafs. how are your shocks?

 

My first thought was the shocks, I replaced them last November with new OEM z71 shocks, pulled both off and they are fine.

Both springs look fine, next weekend the plan is to remove the springs for further inspection of the bushings.