When I did mine just over a year ago, quite a few folks on here were saying "cracked block, get new liners", but I decided to get the heads skimmed and do a gasket job on it - ARP head bolts and all that. I decided I'd chance it was just a head gasket failure (even though to my eye they looked ok when I got them off), rather than the full top-hat liner job.
There was more than one reason why I'd have been justified in suspecting slipping liners - I too had a slight 'lip' when I ran my fingernail across the top of the block to the liner, and the slight appearance of a steam-cleaned cylinder. I still figured I'd chance it.
The bottom line - I saved myself a fortune, and a load of hassle. After it all went back together it has run great (apart from the misfire I've had recently). I've not had a single overheating episode, the top hose is now 'normal' pressure. Just a gasket job solved it all.
Car is a 2000 4.6 P38.
Just thought I'd chuck my experience of it in to the hat....