As a mechanic myself, I change my oil around 3k miles which is typically when it gets dark. It's normal. I'm not a scientist but going to 5-6k shouldn't hurt anything. But I refuse to go 10K miles as some dealers suggest as I've seen the filters split open before then and I've seen the havoc it's wrecked on many vehicles.
I had an Eldorado (4.6) and it burned oil like crazy and also ended up having the dreaded headbolt issue as well, so I passed it on the next person who actually fixed it up. I heavily recommend changing it every 3K miles, and have the cooling system checked with a fine tooth comb. Radiator, hoses, everything. All plastic, all cheap, and more likely to break.
I had an Eldorado (4.6) and it burned oil like crazy and also ended up having the dreaded headbolt issue as well, so I passed it on the next person who actually fixed it up. I heavily recommend changing it every 3K miles, and have the cooling system checked with a fine tooth comb. Radiator, hoses, everything. All plastic, all cheap, and more likely to break.