Usually a severly blown plenum will have liquid oil puddled in it. But I have to say yours looks pretty nasty. There is a simple test you can run with a vacum guage that can check for a blown plenum.
http://dodgeram.info/tsb/2000/09-05-00.htm
Other symptoms include oil consumption (about 1/2 qt every 3000 miles) and pinging under load
How many miles are on your motor? When was the last time it had a major tune up? Has the timing chain every been replaced?
It's really hard to compare a Chevy to a Dodge. The Chevy is much lighter and the TBI 350 makes more hp than a Dodge, however the 2nd gen trucks came out when GM was phasing out thier 5.7 for the 5.3.
I guess I'm not sure what kind of performance boost you are looking for, but a plenum repair and air intake won't do a lot. You might consider saving for a tuner like a SCT that can be reprogramed as you add other mods.
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