The other thought that occurred to me today was that you may have become allergic to something that you have been eating very frequently for a long time.
If a person consumes a food on too regular a basis over a long period of time, it is common to develop an allergy to it.
Some are conscientious about rotating the types of food they eat on a day-to-day basis to avoid developing allergies to anything.
Reflect on the kinds of food you eat every day. Is there something that you eat a couple times a day, each and every day?
I would also recommend giving up drinking ALL soda. Neither diet soda or regular soda are very good for anyone, whether or not they have psoriasis.
The chips and gravy.....well, I'm certain you already know that you shouldn't be consuming that, especially if you are burdened with a skin disorder.
If there was a lot of pepper in the gravy it makes it difficult on the liver to process. Things like pepper, paprika, cinnamon, tumeric, cayenne, etc.. actually tax the liver.
On the other hand, some of those spices I mentioned above, have been found beneficial for the body. Tumeric has been found to have anti-inflammatory and cancer preventative properties. Cinnamon, among many other things, has also been found to be good for digestion and relieving congestion.
Was there any milk added to the gravy?