The album was much more successful than Power from Hell, and is considered a classic by many critics and fanzines. Chris Dahlkvist left the band later in 1986 and was replaced by James Hinder. In 1987, Jase Stallard's guitar playing came into question, so Rockett dismissed him and replaced him with Rob Trotman. Using this line-up, they set out to write material for a third studio album. Having drawn the attention of London Records, the label signed the band. In mid-1988, the band began to start recording their third album, In Search of Sanity. Upon hearing the album, the record label felt that a more versatile vocalist was needed, to do the music more justice. Although the band felt that Sy Keeler's vocals on the demo recording had the right sound, the production had a more polished sound – hence the need for a more polished vocalist. Steve Grimmett, formerly of NWOBHM act Grim Reaper, was drafted in to replace the departing Sy Keeler. Owing to this development, the release of the album was delayed until mid 1989. Following the success of The Force, and with an accomplished new singer, there was much pre-release publicity. In Search of Sanity had a much different sound than Onslaught's previous releases; while it is technically a thrash metal album, it saw them shift towards a progressive/power metal sound, and included the band's longest track to date "Welcome to Dying". Many hardcore thrash metal fans were disappointed with these changes, and this partially contributed to the band's demise. Despite the mixed critical reaction, In Search of Sanity is Onslaught's only album to enter the UK Albums Chart, peaking at No. 46, while the cover version of AC/DC's "Let There Be Rock" was the band's only single to appear in the UK Singles chart, peaking at No. 50. Onslaught toured for over a year in support of In Search of Sanity, playing alongside Annihilator, Xentrix, Slammer, the Crumbsuckers, Horse (not to be confused with the metalcore band from California), Drunken State, Sabbat and Dead On. In early 1990, Steve Grimmett decided to leave the band due to personal reasons, and was replaced by Tony O'Hora. The band then set out to write and then record a fourth album. London Records decided not to renew their contract with Onslaught, leaving the band without a record deal. Roadrunner offered them £50,000 but Rockett declined to sign for