im rebuilding a small road bike, installed a new chain and now the freewheel skips in the smallest 2 gears. i adjusted the rear derailleur as much as i can it lines up perfect and shifts up and down, but acts like its not sized up for the 2 smallest cogs. bike ran perfect on the old rusty chain. what do i need to replace?

skips under load or skips in the stand? skipping under load means worn freewheel

This is par for the course. If the old chain was run until well worn (measure it for stretch if you still have it), the sprockets will be similarly worn and a new chain will skip (disengage and climb over the tops of the sprockets under load).

Usually this happens on the most used or smallest sprockets, but you you'll need a complete new cassette (or freewheel). You can also eyeball it if you have a new cassette to compare to, or by comparing the tooth profile of the smaller worn sprockets to the largest which is usually least worn. If the "U"s between the teeth are visibly broadened at the base, or the teeth appear somewhat asymmetrical the cassette is toast.

thanks, it does only skip under tension, with the bike on its back it seems perfect in everyway.

https://uci.edu/searchResults.php?cx=...bst+brandt#906