Rear Mount gas tank help

[SnowNeck]

Alright, so I have a 1985 gmc high sierra step side, k1500. My gas tank recently started to leak due to a exhaust shop running the pipping to close to the tank. (there fixing it free labor) just have to find the tank... The tank measures 28x22, by like 12 inches in height in the front then slants towards the rear making it round 8 inches in height at the rear of the tank. I cant seem to find the tank anywhere. The previous owner put it in i want to say late 90s maybe early 2000s, its metal and sorta looks like a suburban tank... but doesn't measure up the same. The gas inlet is now located on my rear of my truck right under the tailgate.