Back from living in Auckland, former Central Districts age group player Steward was an obvious selection. Slight and Galpin have worked their way into contention.
In Levin, they each took 3-13 from four overs during the nine wicket win over Hutt Valley in the second T20 match.
Coach Rod Bannister refers to players like this as "bolters".
"Six weeks ago these guys were not even a look in and now they've taken six wickets between them in a rep match."
Bannister said Slight had not put a foot wrong since he was asked to fill in at the pre-season trial last month.
"He brings enthusiasm, energy, a youthful exuberance and he wants to bowl at anyone at anytime - he's a real find.
"Coming from Premier 2 straight into rep cricket has not fazed Slight and he has a very smooth and economical high action.
"Galpin just wants the ball in his hand and wants to bowl, he's vocal in the field and a positive influence for the group," said Bannister.
"You can set a field to him and he's developed a few subtle variations in his bowling over the past 12 months."
In the win over Hutt Valley, which was the first representative victory of any kind for Wanganui in 51 weeks, they bowled the admittedly weak opposition out for 73, with Sam O'Leary also collecting two wickets.
Using their young batsmen, Wanganui's John McIlraith was dismissed for 22 while opening partner Chris Sharrock (35) batted through with Dominic Lock (14) to pick off the runs in the 13th over.
However, there was still a few work-ons after they were beaten by 14 runs in the opening game by hosts Horowhenua Kapiti.
Slight did well as an opening bowler, while Nick Blundell got the ball full and straight, then veteran Mark Fraser came on a difficult time to take two late wickets.
However, Bannister said lacklustre fielding and ability to keep the ball full at the end of the innings let the home side blow through to 145-4.
Carroll (29) and McIlraith (42) got the team off to a good start with a 76-run opening stand, but both were caught out within a short time of each other.
"The lads lost their way from overs 12-16, where they struggled to rotate the strike for too many consecutive balls, at one stage not scoring a run for eight balls in a row," said Bannister.
Fraser (20) and Steward (21) got a few but the run rate lifted quickly to ten-an-over and Wanganui were stranded on 131-6 when stumps were pulled.