Complex sentence: All Tu-154 aircraft models have a relatively high thrust-to-weight-ratio which gave excellent performance, although at the expense of poorer fuel efficiency, which became an important factor in later decades as fuel costs grew.
Split into simpler sentences: All Tu-154 aircraft models have a relatively high thrust-to-weight-ratio which gave excellent performance, at the expense of poorer fuel efficiency. This became an important factor in later decades as fuel costs grew.