You’ve misudnerstood v3/v5
Both v3/v5 use https://api.twitch.tv/kraken/ as the base URL, you specify the version via Header
So to migrate you go
https://api.twitch.tv/kraken/channels/<channel_name>?client_id=<blah>
to
https://api.twitch.tv/kraken/channels/<channel_id>?client_id=<blah>
And send a v5 header
So
curl -H 'Accept: application/vnd.twitchtv.v3+json' \
-H 'Client-ID: uo6dggojyb8d6soh92zknwmi5ej1q2' \
-X GET 'https://api.twitch.tv/kraken/channels/dallas
becomes
curl -H 'Accept: application/vnd.twitchtv.v5+json' \
-H 'Client-ID: uo6dggojyb8d6soh92zknwmi5ej1q2' \
-X GET 'https://api.twitch.tv/kraken/channels/44322889'
Helix is the “new api” which will succeed V5 when V5 gets turned off.
Helix/new API doesn’t currently provide a way to get current game/title when the stream/channel is not live. So The kraken v5 channels end point is the correct solution
See also Kraken V3 → Kraken V5 migration guide: