Frequent truncations are a sign that translation may stall at rare codon positions. Rather than supplementing rare tRNAs (which are challenging to purify), a better strategy is to codon-optimize your template.
Although the mere presence of a rare codon could affect translation efficiency, this is not the only cause of poor translation or truncations. Other factors can have a much larger effect: how many consecutive rare codons are present, target sequence (5’ and 3’ UTR regions, N- or C-terminal tags), template concentration, and incubation conditions.
